C. Nithya

rGO/nano Sb composite: a high performance anode material for Na+ ion batteries and evidence for the formation of nanoribbons from the nano rGO sheet during galvanostatic cycling

Lithium ion batteries exhibit high energy and power densities, thereby making them a promising power sources for multifarious applications. However, the abundance of lithium (Li) is one of the major critical issues for using Li battery technologies. Therefore, for large-scale applications a sodium (Na) ion battery is one of the apt alternatives for portable electronics instead of expensive Li ion batteries. One of the challenging issues in Na+ ion batteries is the difficulty to understand the chemistry involved in view of the large size of the Na+ ion as compared to the Li+ ion, which makes the alloying/dealloying difficult during cycling. Hence, in this present work, we explore an innovative concept of storing Na+ ions in reduced graphene oxide/antimony (Sb) metal composites. Such a concept of storing Na+ in the rGO/Sb composite is one of the simplest ways to enhance the electrochemical performance of metal-based anodes for sodium ion batteries. Furthermore, it is seen that the nano rGO sheet transforms to nanoribbons upon galvanostatic cycling, as evidenced by TEM.

Reduced graphite oxide/nano Sn: a superior composite anode material for rechargeable lithium-ion batteries.

The electrochemical performance of reduced graphite oxide (RGO) anchored with nano Sn particles, which are synthesized by a reduction method, is presented. The Sn nanoparticles are uniformly distributed on the surface of the RGO matrix and the size of the particles is approximately 5-10 nm. The uniform distribution effectively accommodates the volume expansion experienced by Sn particles during cycling. The observed electrochemical performance (97 % capacity retention) can be ascribed to the flexible RGO matrix with uniform distribution of Sn particles, which reduces the lithium-ion diffusion path lengths; therefore, the RGO matrix provides more stability to the Sn particles during cycling. Such studies on Sn nanoparticles anchored on RGO matrices have not been reported to date.

High-Performing LiMgxCuyCo1–x–yO2 Cathode Material for Lithium Rechargeable Batteries

Sustainable power requirements of multifarious portable electronic applications demand the development of high energy and high power density cathode materials for lithium ion batteries. This paper reports a method for rapid synthesis of a cobalt based layered cathode material doped with mixed dopants Cu and Mg. The cathode material exhibits ordered layered structure and delivers discharge capacity of ∼200 mA h g(-1) at 0.2C rate with high capacity retention of 88% over the investigated 100 cycles.

LiCoxMn1‐xPO4/C: A High Performing Nanocomposite Cathode Material for Lithium Rechargeable Batteries

Pristine and Co-doped LiMnPO(4) have been synthesized by the sol-gel method using glycine as a chelating agent and the carbon composites were obtained by the wet ball mill method. The advantage of this method is that it does not require an inert atmosphere (economically viable) and facilitates a shorter time for synthesis. The LiCo(0.09)Mn(0.91)PO(4)/C nanocomposites exhibit the highest coulombic efficiency of 99 %, delivering a capacity of approximately 160 mAhg(-1) and retain a capacity of 96.3 % over the investigated 50 cycles when cycled between 3-4.9 V at a charge/discharge rate of 0.1 C.

High performance NaxCoO2 as a cathode material for rechargeable sodium batteries

Sodium cobalt oxide (NCO) has been synthesized by a glycine assisted sol–gel combustion method. XRD studies confirm the P2 phase formation of NCO. Na exists in two different environments in the NCO crystallite structure, which is confirmed by 23Na Nuclear Magnetic Resonance spectra (NMR). Morphological studies confirm that the particles are unique with a stacked hexagonal shape. Galvanostatic charge/discharge studies performed at different current rates (0.1, 0.2 and 0.5) deliver reversible specific capacities of 126, 108 and 77 mA h g−1 respectively. Further, cycle life performance of the fabricated cells after 50 cycles at 0.1 C rate exhibits an average discharge capacity of ~121 mA h g−1 with a capacity retention of ~86% (Coulombic efficiency ~99.9%). The investigated NCOs superior performance suggests its suitability as a cathode material for Na-ion batteries.

2,3′-Diamino-4,4′-stilbenedicarboxylic acid sensitizer for dye-sensitized solar cells: quantum chemical investigations

The metal-free organic dye sensitizer 2,3′-diamino-4,4′-stilbenedicarboxylic acid has been investigated for the first time for dye-sensitized solar cell applications. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations (performed using the hybrid functional B3LYP) were carried out to analyze the geometry, electronic structure, polarizability, and hyperpolarizability of 2,3′-diamino-4,4′-stilbenedicarboxylic acid used as a dye sensitizer. A TiO2 cluster was used as a model semiconductor when attempting to determine the conversion efficiency of the selected dye sensitizer. Our TD-DFT calculations demonstrated that the twenty lowest-energy excited states of 2,3′-diamino-4,4′-stilbenedicarboxylic acid are due to photoinduced electron-transfer processes. Moreover, interfacial electron transfer between a TiO2 semiconductor electrode and the dye sensitizer occurs through electron injection from the excited dye to the semiconductor’s conduction band. Results reveal that metal-free 2,3′-diamino-4,4′-stilbenedicarboxylic acid is a simple and efficient sensitizer for dye-sensitized solar cell applications.

Effect of donor (tetradecyloxy) and acceptor (carboxamide) groups in trans-stilbene for DSSCs: quantum chemical investigations.

Incorporation of tetradecyloxy and carboxamide groups in trans-stilbene molecule (dye) has been investigated first time for Dye Sensitized Solar Cells (DSSCs) applications. To understand the changes in electronic structure, geometry, dipole moment and polarizability of the mentioned dye architecture has been carried out by using density functional theory (DFT) and time dependent DFT calculations using hybrid functional B3LYP method. Further, the semiconductor TiO2 is also used as a model to evaluate the photo conversion efficiency of the chosen dye architecture. Results reveal that tetradecyloxy and carboxamide groups act as an excellent donor and acceptor groups respectively which give rise to larger difference in excited state dipole moment than the ground state. This kind of stilbene based metal free organic dyes are act as a promising sensitizer for practical DSSCs applications.

Solar powered lithium-ion battery incorporating high performing electrode materials

The development of portable electronic communities requires high performing and high power lithium rechargeable batteries. Herein, we explore a new lithium ion battery combined with a new carbon based anode and cobalt based cathode which delivers an energy output of 280 Wh kg−1 and cycling efficiency of 97% over the investigated 500 cycles (1 C rate) of the lithium ion cell.

Unravel the interaction of protoporphyrin IX with reduced graphene oxide by vital spectroscopic techniques

Probing interaction between dyes and reduced graphene oxide (rGO) is of contemporary research interest. Since, rGO is widely used as electron acceptor in photovoltaic and optoelectronic devices. Hence, we have investigated the interaction between protoporphyrin IX (PPIX) and rGO by vital spectroscopic techniques. The adsorption of PPIX on rGO is studied by Attenuated total reflection-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopic (XPS) measurements. The fluorescence quenching measurements are also performed and the fluorescence intensity of PPIX is quenched by rGO. The quenching of PPIX with rGO is evaluated by the Stern-Volmer equation and time-resolved fluorescence lifetime studies. The results revealed that the fluorescence quenching of PPIX with rGO is due to the static quenching mechanism. The dominant process for this quenching has been attributed to the process of electron transfer from excited state PPIX to rGO. Fluorescence lifetime measurements were used to calculate the rate of electron transfer process between excited state of PPIX and rGO. Transient absorption studies demonstrated the formation of PPIX cation radical for the evidence of electron transfer between PPIX and rGO.

Can the Degree of Crystallinity of Ball Milled Mg2Ni Intermetallic Compound Decide its Electrochemical Characteristics

Nanostructured Mg2Ni intermetallic compounds were synthesised by high energy ball milling. Effect of milling time on structure and surface morphology of milled powders were studied using X-ray diffraction and scanning electron microscopy. Crystallite size and degree of crystallinity were confirmed using transmission electron microscopy and selective area electron diffraction analysis. In order to understand the effect of milling time on reaction rates, Differential Thermal Analysis is performed. Thermal profiles of 30 h milled powders indicate lower activation energy. Cyclic voltammetry, electrochemical impedance spectroscopy and charge-discharge studies were carried out to understand the electrochemical performance of prepared electrode materials. 30 h milled electrode material delivers maximum discharge capacity with superior capacity retention after 20 cycles at 20 mA g-1.