Anatase TiO 2 nanofibers (200-300 nm in diameter) with 3-dimensionally (3D) ordered pore structure and high surface area were synthesized by electrospinning technique. The unique combination of partially acetylacetone chelated Ti-alkoxide, viscosity-controlling cum high positive charge balancing agent PVP and structure director F127 yielded nanofibers with ordered mesoporosity similar to the Pm 3m structure.Dynamic heating of the fibers in the temperature range 350-540 C and simultaneous XRD studies revealed that the amorphous to anatase transformation initiated at about 400 C with the retention of 3D mesoporosity up to the final heat-treatment stage. TEM studies also confirmed this. During amorphous to anatase conversion, the surface area decreased from 165 (350 C) to 90 m 2 g À1 (540 C).The crystalline mesoporous nanofibers showed enhanced photocatalytic activity with reusability.
cycling especially on fast changing rate due to their low lithium intercalation potential (≈0.1 V vs Li/Li + ), resulting the risk of short circuit that may end up with thermal explosion. [7] Whereas, in case of TiO 2 anode materials, not only its relatively high discharge potential (≈1.7 V vs Li/Li + ) suppresses the formation of lithium dendrites but also its low volume expansion during lithiation/delithiation improves long cycling durability and inhibits the formation of solid electrode interface. [8,9] Thus these two aspects of TiO 2 synergistically facilitate superior safety of batteries along with a theoretical capacity of ≈170 mAh g -1 which is comparable with the commercialized cathode material. [10] Additionally, TiO 2 materials are of low cost, nontoxic, chemically and thermally stable. All these properties make TiO 2 advantageous anode material for lithium ion battery application. Unfortunately, the electrochemical performances of TiO 2 is still challenging due to its low electronic conductivity and Li-ion diffusivity inducing a poor rate capability. [11] In addition to that, uses of TiO 2 nanoparticle anodes are restricted by other several issues like particle agglomeration and dissolution during cycling that result in decrease in electroactive area and performance degradation. Present research on this field has made considerable effort to fabricate dimensionally controlled nanostructured TiO 2 with high surface area to enhance the energy storage performances. [12,13] This is because nanostructured materials offer shortening of Li + diffusion path, large interfacial active area, and also possess the ability to relax the strain generated during Li + insertion/extraction process. [14][15][16] In this perspective 1D nanomaterials such as nanotubes or nanofibers are good choice to satisfy all these criteria due to their large specific surface area and high aspect ratio (surface to volume ratio) which assure favorable transport of both the electrons and Li + . [3,17,18] On the other side, porosity within the structure not only enables high rate capability by decreasing the polarization resistance but also it allows easy access of active sites for Li + , electrons and electrolyte resulting improved kinetics favorable for better cycle performance and storage capacity. [19][20][21] Moreover, Li storage performances in The authors report a novel strategy to fabricate electrospun anatase TiO 2 -rGO composite nanofibers with 3D cubic ordered mesoporosity. Such synthesis route not only ensures molecular level composite formation between rGO and TiO 2 but also retains the rGO content and orders mesostructure after calcination of the nascent fiber at an optimum condition that only removes the surfactant and polymer. Transmission electron microscopic and low angle X-ray diffraction studies confirm the presence of ordered mesoporosity within the nanofibers. Raman and X-ray photoelectron spectroscopy studies reveal the molecular level composite formation between rGO and TiO 2 with chemical bonding. This composite nano...
Development of advanced carbon cathode support with the ability to accommodate high sulfur (S) content as well as effective confinement of the sulfur species during charge–discharge is of great importance for sustenance of Li–S battery. A facile poly(vinylpyrrolidone)-assisted solvothermal method is reported here to prepare Mg–1,4-benzenedicarboxylate metal organic framework (MOF) from which mesoporous carbon is derived by thermal treatment, where the hexagonal sheetlike morphology of the parent MOF is retained. Existence of abundant pores of size 4 and 9 nm extended in three dimensions with zigzag mazelike channels helps trapping of S in the carbon matrix through capillary effect, resulting in high S loading. When tested as a cathode for lithium–sulfur battery, a reversible specific capacity of 1184 mAh g –1 could be achieved at 0.02 C. As evidenced by X-ray photoelectron spectroscopy, in situ generated Mg in the carbon structure enhances the conductivity, whereas MgO provides support to S immobilization through chemical interactions between Mg and sulfur species for surface polarity compensation, restricting the dissolution of polysulfide into the electrolyte, the main cause for the “shuttle phenomenon” and consequent capacity fading. The developed cathode shows good electrochemical stability with reversible capacities of 602 and 328 mAh g –1 at 0.5 and 1.0 C, respectively, with retentions of 64 and 67% after 200 cycles. The simple MOF-derived strategy adopted here would help design new carbon materials for Li–S cathode support.
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