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

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

Capacity Enhancement of the Quenched Li-Ni-Mn-Co Oxide High-voltage Li-ion Battery Positive Electrode

Li-rich metal oxides, regarded as a high-voltage composite cathode, is currently one of the hottest positive electrode material for lithium-ion batteries, due to its high-capacity and high-energy performance. The crystallography, phase composition and morphology can be altered by synthesis parameters, which can influence drastically the capacity and cycling performance. In this work, we demonstrate Li1.207Ni0.127Mn0.54Co0.127O2, obtained by a co-precipitation method, exhibits super-high specific capacity up to 298 mAh g−1 and excellent capacity retention of ∼100% up to 50 cycles. Using neutron powder diffraction and transmission X-ray microscopy, we have found that the cooling-treatments applied after sintering during synthesis are crucially important in controlling the phase composition and morphology of the cathodes, thereby influencing the electrochemical performance. Unique spherical microstructure, larger lattice, and higher content of Li-rich monoclinic component can be achieved in the rapid quenching process, whereas severe particle cracking along with the smaller lattice and lower monoclinic component content is obtained when natural cooling of the furnace is applied. Combined with electrochemical impedance spectra, a plausible mechanism is described for the poorer specific capacity and cycling stability of the composite cathodes