School of Engineering Sciences and Technology

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Browsing School of Engineering Sciences and Technology by Author "Adams, S."
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    Exfoliated Graphene Oxide/MoO < inf > 2 < /inf > Composites as Anode Materials in Lithium-Ion Batteries: An Insight into Intercalation of Li and Conversion Mechanism of MoO < inf > 2 < /inf >
    ( 2016-05-04) Petnikota, Shaikshavali ; Teo, Keefe Wayne ; Chen, Luo ; Sim, Amos ; Marka, Sandeep Kumar ; Reddy, M. V. ; Srikanth, V. V.S.S. ; Adams, S. ; Chowdari, B. V.R.
    Exfoliated graphene oxide (EG)/MoO2 composites are synthesized by a simple solid-state graphenothermal reduction method. Graphene oxide (GO) is used as a reducing agent to reduce MoO3 and as a source for EG. The formation of different submicron sized morphologies such as spheres, rods, flowers, etc., of monoclinic MoO2 on EG surfaces is confirmed by complementary characterization techniques. As-synthesized EG/MoO2 composite with a higher weight percentage of EG performed excellently as an anode material in lithium-ion batteries. The galvanostatic cycling studies aided with postcycling cyclic voltammetry and galvanostatic intermittent titrations followed by ex situ structural studies clearly indicate that Li intercalation into MoO2 is transformed into conversion upon aging at low current densities while intercalation mechanism is preferably taking place at higher current rates. The intercalation mechanism is found to be promising for steady-state capacity throughout the cycling because of excess graphene and higher current density even in the operating voltage window of 0.005-3.0 V in which MoO2 undergoes conversion below 0.8 V.
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    Experimental Elucidation of a Graphenothermal Reduction Mechanism of Fe < inf > 2 < /inf > O < inf > 3 < /inf > : An Enhanced Anodic Behavior of an Exfoliated Reduced Graphene Oxide/Fe < inf > 3 < /inf > O < inf > 4 < /inf > Composite in Li-Ion Batteries
    ( 2017-02-23) Petnikota, Shaikshavali ; Maseed, Hussen ; Srikanth, V. V.S.S. ; Reddy, M. V. ; Adams, S. ; Srinivasan, Madhavi ; Chowdari, B. V.R.
    The graphenothermal reduction mechanism of Fe2O3 by graphene oxide (GO) is elucidated through careful experimental analysis. The degree of oxidation (DO) of GO plays a key role in controlling the reduction of Fe2O3 by GO. GO with low DO follows a conventional three-stage reaction path, i.e., ′2GO + Fe2O3 → EG/Fe3O4 (Stage I) → EG/FeO (Stage II) → EG/Fe (Stage III)′ (where EG is exfoliated reduced graphene oxide), at temperatures 650 and 750°C to reduce Fe2O3, whereas the GO with higher DO transforms rapidly and ceases the reduction at Stage I, i.e., with the formation of EG/Fe3O4 at 650°C. It is also found that slow thermal treatment of GO continues the reduction to Stage II and further to Stage III depending on time of heating and temperature. EG/Fe3O4 (synthesized at 550°C, 5 h) by using GO with low DO showed superior cycling performance as an anode of Li-ion battery than its counterpart prepared (at 650°C, 5 h) from GO with high DO owing to good contacts between EG and Fe3O4. EG/Fe3O4 (synthesized at 550°C, 5 h) exhibited reversible capacity as high as 860 mAh/g which is greater than the specific capacity of EG/Fe3O4 synthesized (at 650°C, 5 h) by 150 mAh/g. Overall, EG/Fe3O4 (synthesized at 550°C, 5 h) outperformed its counterpart (i.e., EG/Fe3O4 synthesized at 650°C, 5 h) by exhibiting excellent cycling stability and rate capability at current rates ranging from 0.5 to 3.0 C. (Chemical Equation Presented).
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    Sustainable Graphenothermal Reduction Chemistry to Obtain MnO Nanonetwork Supported Exfoliated Graphene Oxide Composite and its Electrochemical Characteristics
    ( 2015-10-22) Petnikota, Shaikshavali ; Srikanth, Vadali V.S.S. ; Nithyadharseni, P. ; Reddy, M. V. ; Adams, S. ; Chowdari, B. V.R.
    Exfoliated graphene oxide (EG)/manganese(II) oxide (MnO) composite powder is synthesized by simple solid state graphenothermal reduction process. Structural, chemical, and morphological studies confirm the formation of EG/MnO composite in which cubic MnO crystallites are found to anchor onto EG surfaces. The as-synthesized EG/MnO composite is constituted with 65 and 35 wt % of MnO and EG, respectively. The EG/MnO composite exhibits a specific surface area of ∼82 m2 g-1 and an average pore size of ∼12 nm. As an anode in lithium-ion batteries, the EG/MnO composite shows a high reversible capacity of 936 mAh g-1 at a current rate of 75 mA g-1. Capacity retention of ∼84% (784 mAh g-1) is observed even at the 100th cycle which corresponds to a Coulombic efficiency of ∼99%. Cyclic voltammetry studies on the composite show that Li storage is owing to reversible conversion reactions of MnO and electrochemical absorption/desorption by EG. Electrochemical impedance spectroscopy studies clearly show easy lithiation kinetics. Owing to the electrochemical performance of EG/MnO composite and its easy, reproducible, and scalable synthesis procedure, it is an excellent addition to this class of similar materials.