Soumen Giri

Synthesis, characterization and electrochemical performance of graphene decorated with 1D NiMoO4·nH2O nanorods

One-dimensional NiMoO4 · nH2O nanorods and their graphene based hybrid composite with good electrochemical properties have been synthesized by a cost effective hydrothermal procedure. The formation of the mixed metal oxide and the composite was confirmed by XRD, XPS and Raman analyses. The morphological characterizations were carried out using FESEM and TEM analyses. The materials were subjected to electrochemical characterization through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) studies with 6 M KOH as the supporting electrolyte. For NiMoO4 · nH2O, a maximum specific capacitance of 161 F g(-1) was obtained at 5 A g(-1) current density, accompanied with an energy density of 4.53 W h kg(-1) at a steady power delivery rate of 1125 W kg(-1). The high utility of the pseudocapacitive NiMoO4 · nH2O was achieved in its graphene based composite, which exhibited a high specific capacitance of 367 F g(-1) at 5 A g(-1) current density and a high energy density of 10.32 W h kg(-1) at a power density of 1125 W kg(-1) accompanied with long term cyclic stability.

Polyaniline-wrapped 1D CoMoO4·0.75H2O nanorods as electrode materials for supercapacitor energy storage applications

In this study, a simple and cost effective one-pot hydrothermal process has been carried out for the synthesis of 1D CoMoO4·0.75H2O nanorods. A binary composite of CoMoO4·0.75H2O/PANI has also been synthesized by the in situ oxidative polymerization of aniline with virgin CoMoO4·0.75H2O. Two types of PANI morphologies have been demonstrated: amorphous nanodimensional PANI uniformly coated on CoMoO4·0.75H2O nanorods, and interconnected hollow spheres like PANI inside the bulk material. The prepared CoMoO4·0.75H2O/PANI composite was characterized by X-ray diffraction analysis and Fourier transform infrared spectroscopy for the phase and formation, respectively. The surface morphology was investigated by using FESEM and TEM, which revealed the formation of the CoMoO4·0.75H2O/PANI composite. The electrochemical characterization of the pseudocapacitive CoMoO4·0.75H2O and CoMoO4·0.75H2O/PANI composites in 1 M Na2SO4 showed the highest specific capacitances of 285 F g−1 and 380 F g−1, respectively, at a current density of 1 A g−1. The cyclic stability test demonstrated the specific capacitance retention of about 90.4% after 1000 consecutive charge–discharge cycles at a constant current density of 1 A g−1, which is also higher than that of virgin CoMoO4·0.75H2O—86.3% retention of specific capacitance.

Pyrazine Functionalized Ag(I) and Au(I)-NHC Complexes are Potential Antibacterial Agents

Antimicrobial resistance is an ever-increasing problem throughout the world and has already reached severe proportions. Bacteria can develop ways to render traditional antibiotics ineffective, raising a crucial need to find new antimicrobials with novel mode of action. We demonstrate here a novel class of pyrazine functionalized Ag(I) and Au(I)-NHC complexes as antibacterial agents against human pathogens that are resistant to several antibiotics. Complete synthetic and structural studies of Au(I) and Ag(I) complexes of 2-(1-methylimidazolium) pyrimidinechloride (L-1), 2,6-bis(1-methylimidazol)pyrazinechloride (L-2) and 2,6-bis(1-methyl imidazol) pyrazinehexa-fluorophosphate (L-3) are reported herein. Chloro[2,6-bis(1-methyl imidazol)pyrazine]gold(I), 2b and chloro [2,6-bis(1-methyl imidazol)pyrazine]silver(I), 2a complexes are found to have more potent antimicrobial activity than other synthesized compounds and several conventionally used antibiotics. Complexes 2b and 2a also inhibit the biofilm formation by Gram-positive bacteria, Streptococcus mutans and Gram-negative bacteria, Escherichia coli, causing drastic damage to the bacterial cell wall and increasing membrane permeability. Complexes 2b and 2a strongly binds to both Lys and Dap-Type peptidoglycan layers, which may be the reason for damage to the bacterial cell wall. Theoretical studies of all the complexes reveal that 2b and 2a are more reactive than other complexes, and this may be the cause of differences in antibacterial activity. These findings will pave the way towards developing a new class of antibiotics against different groups of conventional antibiotic-resistant bacteria.

Theoretical investigation of hydrogen adsorption in all-metal aromatic clusters

Molecular hydrogen adsorption in binary all-metal aromatic systems has been explored using ab initio quantum chemical calculations. For this study, we have considered different classes of bimetallic clusters, viz. Be3M2, Mg3M2 and Al4M2 (M = Li, Na and K). In all these bimetallic clusters, the interaction energies of the alkali metal ion with the base metal surface are quite high and the alkali metal sites are found to carry partial positive charges which enhance the adsorption enthalpies of molecular hydrogen on them. Among the three classes considered here, Mg3M2 are found to have poor hydrogen adsorption enthalpies as compared to the other two classes due to less charge on the alkali metals. Although the charge developed on K is more than that developed on Li and Na, the hydrogen adsorption in Be3K2 and Al4K2 is found to be weak in comparison to their Li and Na doped counterparts. In the case of Be3Li2 and Be3Na2, the hydrogen adsorption energies are found to be quite comparable to the optimum adsorption energy proposed for ambient temperature hydrogen storage and the gravimetric density of hydrogen is found to be 22.64 and 14.12 wt% respectively, with three H2 molecules adsorbed per alkali metal atom. In the case of Al4M2, the positive charges on the alkali metal atoms as well as the hydrogen adsorption energies are found to be higher as compared to those in Be3M2 clusters. The gravimetric densities of hydrogen in hydrogenated Al4Li2 and Al4Na2 are found to be respectively 11.59 and 9.4 wt% with four H2 molecules adsorbed per alkali metal atom.

One pot synthesis of ilmenite-type NiMnO3-"nitrogen-doped" graphene nanocomposite as next generation supercapacitors.

NiMnO3-nitrogen doped graphene composite has been synthesized by a simple hydrothermal method and its supercapacitor performance investigated. The composite exhibits a specific capacitance of 750.2 F g(-1) in 1 M Na2SO4 at a scan rate of 1 mV s(-1). Nitrogen insertion inside the carbon lattice plays a crucial role in the enhancement of the overall specific capacitance and its long-term stability. This reproducible and superior performance of NiMnO3-nitrogen doped graphene composite make it attractive as a candidate for energy storage materials.

Supercapacitor based on H+ and Ni2+ co-doped polyaniline–MWCNTs nanocomposite: synthesis and electrochemical characterization

In the search for promising electrode materials for supercomputer applications, we have synthesized a Ni2+ doped polyaniline, and a nanocomposite based on multiwalled carbon nanotubes (MWCNTs) and a Ni2+ doped polyaniline (PANI) in a HCl medium by an in situ oxidative polymerization. In the HCl medium and in the presence of Ni2+, PANI becomes co-doped with both H+ and Ni2+. The as synthesized materials were characterized by FTIR and Raman spectroscopy and an XRD study. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses confirmed the successful coating of the co-doped PANI on the MWCNT surface. The electrochemical characterizations were carried out by a three electrode system, with 1 M H2SO4 as the electrolyte. The PANI co-doped with H+ and Ni2+exhibited a specific capacitance of 311 F g−1 at a 0.5 A g−1 constant current, which was higher than that of the solely H+ doped PANI, which exhibited a specific capacitance of 265 F g−1 under the same conditions. The incorporation of MWCNTs to the co-doped PANI influenced the specific capacitance to increase to 781 F g−1 at the same constant current density, with a 92% retention of initial specific capacitance over 700 galvanostatic cycles.

High performance supercapacitor electrode material based on vertically aligned PANI grown on reduced graphene oxide/Ni(OH)2 hybrid composite

A simple and cost effective one pot hydrothermal process has been followed for the synthesis of flowery Ni(OH)2, reduced graphene oxide (rGO)/Ni(OH)2 hybrid composite. A ternary composite of rGO/Ni(OH)2/PANI has also been synthesised by in situ oxidative polymerisation of aniline with the binary composite of rGO/Ni(OH)2. A unique morphology of vertically aligned PANI on rGO surface and randomly connected PANI nanowires has been demonstrated following a heterogeneous nucleation on the rGO surface and homogeneous nucleation inside the bulk material. A comparative electrochemical analysis reveals a superior electrochemical behavior of the ternary composite over the rGO–Ni(OH)2, which again shows better electrochemical utility over the virgin Ni(OH)2. The proton insertion/deinsertion reversible pseudocapacitance of Ni(OH)2 combined with the pseudocapacitance of the vertically aligned conducting PANI nanowires and their synergistic effect with in situ reduced graphene oxide results in a high specific capacitance of 514 F g−1 at 2 A g−1 current density accompanied with 94.4% specific capacitance retention after 1000 charge discharge cycles at 5 A g−1 current density.

In Situ Synthesis of Graphene/Amine-Modified Graphene, Polypyrrole Composites in Presence of SrTiO3 for Supercapacitor Applications

Composites based on both unmodified and amine-modified graphene were successfully prepared via in situ oxidative polymerization of pyrrole in presence of SrTiO3. To characterize the graphene/amine-modified graphene-polypyrrole-SrTiO3 composite electrodes, cyclic voltammetry test for measuring specific capacitance, cyclic charge discharge test and an ac impedance test were executed. The composite with unmodified graphene showed better specific capacitance but a little lower cyclability compared to that of modified graphene composite. The presence of SrTiO3 ensures the better thermal stability of the composites compared to that of simple graphene–polypyrrole composite.

Dirichlet boundary conditions and effect of confinement on chemical reactivity.

To understand the source of discrepancy in the qualitative trends in the reactivity of the spherically confined atoms/ions when the high pressure is generated through the use of a proper Dirichlet boundary condition [J. Chem. Sci. 2005, 117, 379; Phys. Chem. Chem. Phys. 2008, 10, 1406] and of a cutoff function [Chem. Phys. Lett. 2003, 372, 805; J. Phys. Chem. A 2003, 107, 4877], a modified Herman-Skilman program is run. Results obtained from different formulas of reactivity parameters are analyzed. Change in reactivity for different electronic configurations is also reported. It is observed that the use of different formulas is the major source of discrepancy and not the Dirichlet condition, although the latter is highly recommended. As the cutoff radius of the confining spherical box decreases, the energy of the atom/ion increases, the electronegativity decreases, and the hardness increases and ultimately slightly decreases in an ultraconfined situation. For small R(C) values, softness decreases and electrophilicity increases and attains relatively small values. The reactivity of confined atoms/ions is put in a proper perspective.

STUDY OF COPPER FERRITE NANOWIRE FORMATION IN PRESENCE OF CARBON NANOTUBES AND INFLUENCE OF FLUORINATION ON HIGH PERFORMANCE SUPERCAPACITOR ENERGY STORAGE APPLICATION

Supercapacitors are highly attractive energy storage device of the modern world. It can supply peak pulse power and high cycle stability to an electrochemical system. Here, we have explored the formation of copper ferrite (CuFe2O4) nanowire formation in presence of carbon nanotubes (CNTs) and enhancement of electrochemical performance on fluorination. All the electrochemical characterization was studied by three electrode system. Fourier transform infrared spectroscopy (FT-IR) was performed to test the functionality present in the composite. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) study had been carried out to observe the change in surface and bulk morphology of the composites which showed that CuFe2O4 nanowires are attached with CNTs or fluorinated CNTs. This fluorinated nanocomposite shows the highest specific capacitance of 267 F/g.