Vertically-aligned graphene nanowalls grown via plasma-enhanced chemical vapor deposition as a binder-free cathode in Li-O_2 batteries

In the present report, vertically-aligned graphene nanowalls are grown on Ni foam (VA-G/NF) using plasma-enhanced chemical vapor deposition method at room temperature. Optimization of the growth conditions provides graphene sheets with controlled defect sites. The unique architecture of the vertically-aligned graphene sheets allows sufficient space for the ionic movement within the sheets and hence enhancing the catalytic activity. Further modification with ruthenium nanoparticles (Ru NPs) drop-casted on VA-G/NF improves the charge overpotential for lithium–oxygen (Li–O_2) battery cycles. Such reduction we believe is due to the easier passage of ions between the perpendicularly standing graphene sheets thereby providing ionic channels

Vertically-aligned graphene nanowalls grown via plasma-enhanced chemical vapor deposition as a binder-free cathode in Li-O_2 batteries

In the present report, vertically-aligned graphene nanowalls are grown on Ni foam (VA-G/NF) using plasma-enhanced chemical vapor deposition method at room temperature. Optimization of the growth conditions provides graphene sheets with controlled defect sites. The unique architecture of the vertically-aligned graphene sheets allows sufficient space for the ionic movement within the sheets and hence enhancing the catalytic activity. Further modification with ruthenium nanoparticles (Ru NPs) drop-casted on VA-G/NF improves the charge overpotential for lithium–oxygen (Li–O_2) battery cycles. Such reduction we believe is due to the easier passage of ions between the perpendicularly standing graphene sheets thereby providing ionic channels

Pressure-Controlled Chemical Vapor Deposition of Graphene as Catalyst for Solar Hydrogen Evolution Reaction

In the present report, graphene-based catalysts on silicon substrate have been examined as the photocathode for solar hydrogen evolution reaction (HER). Mono-layered graphene has been synthesized through low-pressure chemical vapor deposition (LPCVD), whereas multi-layered graphene has been synthesized by atmospheric pressure chemical vapor deposition (APCVD). Copper foil is used as the substrate. The graphene layer on Cu foil subsequently transferred on to silicon photoabsorber using poly(methyl-2-methylpropenoate) (PMMA). At the initial linear sweep voltammetry (LSV) scan, LPCVD-synthesized graphene-Si (LPCVD-Si) electrode showed an onset potential of −0.65 V and photocurrent of −4.31 mA cm^(−2) (at −0.385 V). On the contrary, the onset potential and photocurrent of APCVD-prepared graphene-Si (APCVD-Si) photocathode are −0.36 V and −28.28 mA cm^(−2) (at −0.385 V), respectively. After the 130th LSV scan, the onset potential and photocurrent of LPCVD-Si improved to −0.39 V and −13.28 mA cm^(−2) (at −0.385 V), respectively. In addition, the onset potential and photocurrent of APCVD-Si photocathode at the LSV 130th scan are enhanced to −0.36 V and −28.28 mA cm^(−2) (at −0.385 V), respectively. The graphene sample grown via LPCVD-Si show stable performance whereas, the graphene obtained via APCVD-Si have higher photocurrent poor stability

Microwave-Assisted Synthesis of NiO Nanoparticles

NiO has been synthesized by microwave-induced chemical synthesis route using metalorganic complex of nickel in a domestic-type microwave oven (2.45 GHz). A novel metalorganic complex of nickel, viz., a beta-ketoester of nickel, synthesized and characterized as apart of this work, was employed as the precursor material. We varied the experimental parameters, such as the choice of solvent and microwave power, to obtain nanoparticles of NiO. The NiO nanoparticles were characterized by XRD, SEM, and TEM. The particle size of the NiO was found to vary from 7-40 nm. The magnetic behavior of the nanoparticles of NiO was examined with a vibrating sample magnetometer, revealing that as the particle size diminishes, the magnetic ordering in NiO changes, leading to a small, measurable coercivity

Metal-organic chemical vapor-deposited cobalt oxide films as negative electrodes for thin film Li-ion battery

In this study, thin films of cobalt oxide (Co3O4) have been grown by the metal-organic chemical vapor deposition (MOCVD) technique on stainless steel substrate at two preferred temperatures (450 degrees C and 500 degrees C), using cobalt acetylacetonate dihydrate as precursor. Spherical as well as columnar microstructures of Co3O4 have been observed under controlled growth conditions. Further investigations reveal these films are phase-pure, well crystallized and carbon-free. High-resolution TEM analysis confirms that each columnar structure is a continuous stack of minute crystals. Comparative study between these Co3O4 films grown at 450 degrees C and 500 degrees C has been carried out for their application as negative electrodes in Li-ion batteries. Our method of electrode fabrication leads to a coating of active material directly on current collector without any use of external additives. A high specific capacity of 1168 micro Ah cm(-2) mu m(-1) has been measured reproducibly for the film deposited at 500 degrees C with columnar morphology. Further, high rate capability is observed when cycled at different current densities. The Co3O4 electrode with columnar structure has a specific capacity 38% higher than the electrode with spherical microstructure (grown at 450 degrees C). Impedance measurements on the Co3O4 electrode grown at 500 degrees C also carried out to study the kinetics of the electrode process. (C) 2014 Published by Elsevier B.V

Morphology Controlled Growth of Meso-Porous Co3O4 Nanostructures and Study of Their Electrochemical Capacitive Behavior

The morphology of nanocrystalline Co3O4 synthesized through microwave irradiation of a solution of a cobalt complex is found to depend reproducibly on the conditions of synthesis and, in particular, on the composition of the solvent used. Despite the rapidity of the process, oriented aggregation occurs under certain conditions, depending on solvent composition. Annealing the oriented samples leads to microstructures with significant porosity, rendering the material suitable as electrodes for electrochemical capacitors. Electrochemical analysis of the oxide samples was carried out in 0.1M Na2SO4 electrolyte vs. Ag/AgCl electrode. A stable specific capacitance of 221 F/g was measured for a meso-porous sample displaying oriented aggregation. Stability of these oxide materials were checked for longer charge-discharge cycling. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.002210jes] All rights reserved

VS2/rGO hybrid nanosheets prepared by annealing of VS4/rGO

Layered transition metal dichalcogenides and their hybrids with reduced grpahene oxide (rGO) have attracted much interest due to many potential applications for electrode materials in Li ion batteries and supercapacitors and electro-catalysts for hydrogen evolution reaction. Among them, synthesis of VS2 sheets and VS4/rGO hybrid via a hydrothermal reaction was recently reported, whereas VS2/rGO hybrid sheets have not been reported. In this study, we report VS2/rGO hybrid sheets after annealing VS4/rGO hybrid materials at 350 ??C. The conversion of VS4 to VS2 on rGO sheets after annealing is attributed to a thermal cleavage of VS4.close

Flower-like porous cobalt(II) monoxide nanostructures as anode material for Li-ion batteries

In the present study, a microwave-assisted, solution-based route has been employed to obtain porous CoO nano structures. Detailed characterization reveals that the flower-like nanostructures comprise petal-like sheets, each of which is made of an ordered, porous arrangement of crystallites of CoO measuring about 6 nm. TEM analysis shows that each ``petal'' is an oriented aggregate of CoO nanocrystals, such aggregation promoted by the hydroxyl moieties derived from the solution. The structure provides a large specific area as well as the porosity desirable in electrodes in Li-ion batteries. Electrochemical measurements carried out on electrodes made of nanostructured CoO show excellent Li ion-storing capability. A specific capacitance of 779 mAh g(-1) has been measured at a specific current of 100 mA g(-1). Measurements show also excellent cyclability and coulombic efficiency. Impedance spectroscopy provides evidence for charge transfer occurring in the porous networks. (C) 2015 Elsevier B.V. All rights reserved

Voltammetric Enhancement of Li-Ion Conduction in Al-Doped Li7-xLa3Zr2O12 Solid Electrolyte

2017 American Chemical Society. Al-doped Li 7-x La 3 Zr 2 O 12 is found to be more ionically conductive following voltammetric treatment in an all-solid-state Li|Li 7-x La 3 Zr 2 O 12 |Li cell configuration. This result is consistent with electrical impedance spectroscopy measurements, which reveal that the activation energy for lithium diffusion is reduced from 0.32 to 0.26 eV following voltammetric treatment. The Li deposition-dissolution signal has been observed in the voltammograms, and neutron powder diffraction shows an increase in the lithium content of the Li 7-x La 3 Zr 2 O 12 . Furthermore, X-ray photoelectron spectroscopy indicates a local rearrangement of O, resulting in a reduction of defects following voltammetric treatment, with the enhanced conductivity attributable to both the reduction of defect oxygen and increased lithium content. This work, therefore, reveals such voltammetric treatment as a simple and inexpensive alternative to existing doping approaches to boost the electrochemical performance of Li 7-x La 3 Zr 2 O 12 . The findings can improve the future development of all-solid-state Li-ion batteries. On the other hand, our approach to understanding the conductivity enhancement via voltammetric treatment may provide a better alteration in the ionic conduction of solid electrolytes during solid-state battery operation. (Graph Presented)

Bis(tert-butyl-3-oxobutanoato)dipyridinenickel(II) benzene solvate

The title compound, [ Ni( C8H13O3)(2)( C5H5N)(2)]center dot C6H6, a potential metal-organic chemical vapour deposition ( MOCVD) precursor, crystallizes with half a molecule of the complex and half a molecule of benzene in the asymmetric unit, both molecules being centrosymmetric. The Ni atom is at the origin ( 0, 0, 0), while the centroid of the benzene solvent molecule is at another centre of symmetry ( 0, 1 2, 1 2). The Ni atom has a distorted octahedral environment, with four O atoms from the bidentate tert-butyl-3-oxobutanoate ligand units in the axial positions and the two N atoms of the pyridine ligands at the apical positions. C-H center dot center dot center dot pi contacts [ 3.021 ( 4) angstrom] between solvent benzene and the pyridine ligand, along with pi-pi stacking interactions [ 3.896 ( 1) angstrom] between adjacent pyridine ligands, result in a packing motif along the c axis