Totally found 1824 items.

  • [期刊] Effect of hydrogen-gas treatment on the local structure of graphene-like graphite
    Graphene-like graphite (GLG) has been expected as a new candidate for a large-capacity negative electrode material of a lithium-ion battery. Recently, our group has reported that hydrogen-gas treatment of GLG lowered the mean-discharge potential and increased its capacity. In order to clarify the origin of this improvement, scanning tunneling microscopy (STM) was conducted together with simulation using density functional theory calculation. A GLG mono-sheet suitable for STM observation was synthesized from highly oriented pyrolytic graphite (HOPG) as a raw material. A distorted honeycomb region surrounded by triangular one was observed for GLG mono-sheets and it was well simulated using a model consisting of a topmost graphene with pairwisely introduced ether groups underneath. The above honeycomb region disappeared for GLG treated with hydrogen gas (GLG-H), and it was also well simulated using a model in which each oxygen atom introduced in the graphene was substituted by two hydrogen atoms. Since the resulting local structure of GLG-H was similar to that of graphite which shows low discharge potential, this would lead to the increased accessible capacity under 2.0 V of cut-off voltage. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Fabrication of superelastic and highly conductive graphene aerogels by precisely "unlocking" the oxygenated groups on graphene oxide sheets
    Oxygenated groups in graphene oxide (GO) have significant influences on the physicochemical properties of GO. Accurate identification and manipulation of oxygenated groups should be essential for sheets functionalization and assembly, but remains challenging. Herein a novel design of oxygenated groups on GO via a facile alkali-annealing strategy is reported to rationally "unlock" specific groups and increase covalent bonding density on sheets. The structural evolution of epoxy and enriched in hydroxyl are well monitored and verified. Based on the fact that hydroxyl is widely regarded as active sites for cross-linker polyvinyl alcohol, a well interweaved graphene aerogel (GA) with ordered "layer-strut" bracing architectures is successfully fabricated. The constructed GA possesses an ultralow density of 1.73 mg cm(-3), exceptional resilience with 85% compressive strength recovery even after 1000 cycles, and high conductivity of 17.1 S m(-1), demonstrating the significantly reinforced interplays between adjacent layers. The highest specific conductivity (sigma/rho) of the optimized GA reaches 98.8 S cm(2) g(-1), which is far superior to conventional GA assembled by GO in as-prepared form and exceeding most graphene-based aerogels reported. This new insight into precise engineering oxygenated structures will provide inspirational ideas towards more elaborate graphene-related architectures and a better overall understanding of GO structure. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Strain-controlled magnetic ordering in 2D carbon metamaterials
    We use ab initio spin-polarized density functional theory to study the magnetic order in a Kagome-like 2D metamaterial consisting of pristine or substitutionally doped phenalenyl radicals polymerized into a nanoporous, graphene-like structure. In this and in a larger class of related structures, the constituent polyaromatic hydrocarbon molecules can be considered as quantum dots that may carry a net magnetic moment. The structure of this porous system and the coupling between the quantum dots may be changed significantly by applying moderate strain, thus allowing to control the magnetic order and the underlying electronic structure. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Sintered Fe/CNT framework catalysts for CO2 hydrogenation into hydrocarbons
    Because of its contribution to greenhouse effect, carbon dioxide conversion to valuable chemicals is one of the most challenging issues facing the modern world. A new type of iron catalysts of CO2 hydrogenation into hydrocarbons was synthesized by spark plasma sintering of carbon nanotubes decorated with iron oxide nanoparticles. This treatment produced carbon-encapsulated iron nanocrystals embedded in a dense framework of CNTs. The sintered catalysts were tested without pre-reduction in CO2 hydrogenation under supercritical conditions (350 degrees C, 8.5 MPa) and showed high specific activities of 5.4-12.2 mol(CO2)g(Fe)(-1)s(-1) and promising C2+ selectivities of 40-50 mol.% at rather low H-2:CO2 ratios of 1 and 2. The high efficiency of the catalysts was attributed to the stabilization of metal nanoparticles by carbon shells and increased density of CNT support, which led to higher degree of metal - support interaction and intensified carbidization and CO activation. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Low-temperature growth of carbon shells on gold and copper nanoparticles inside a transmission electron microscope
    Assisted by electron beam irradiation in a transmission electron microscope chamber, carbon shells are grown on both gold (Au) and copper (Cu) nanoparticles at low temperatures. Using single-walled carbon nanotube film as support, it is observed that graphene shells can nucleate on Au nanoparticles at 350 degrees C and at a temperature as low as 150 degrees C on Cu nanoparticles. The low temperature carbon assembly is attributed to a truncated graphene formation pathway, low reaction barriers and exothermic reaction processes. The calculated energy barriers for graphene assembly from active carbon atoms on Au (111) and Cu (111) surfaces are 0.57 eV and 0.44 eV, respectively, which are roughly 1/3 of the barriers for carbon source dissociation. On the one hand, the decomposition of hydrocarbon molecules is entirely driven by the electron collision-induced radiolysis reaction and thus does not contribute to the graphene formation energetics. On the other hand, the feasible nucleation process ensures the synthesis of carbon shells at low temperature in view of both kinetics and thermodynamics. This work not only opens a new avenue for low temperature synthesis of graphitic shells, but also helps to understand the growth mechanisms of graphene encapsulated materials. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Inhibited corrosion activity of biomimetic graphene-based coating on Mg alloy through a cerium intermediate layer
    The poor corrosion/wear resistance of Mg alloy seriously limits its industrial application. Graphene-based anti-corrosion coatings show the excellent imperviousness, but they can provide the additional cathodic sites for Mg alloys, which accelerates the galvanic corrosion behaviors near the interfaces. A novel design of cerium-based intermediate layer (Ce(IV)) is reported in this study, which exhibits a synergistic effect of hydrogen/ionic bond on the graphene oxide (GO)/polyvinyl alcohol (PVA) biomimetic coating. It overcomes the problems of galvanic corrosion and low interfacial adhesion between Mg substrate and hybrid coating through a prominent barrier effect. Furthermore, the GO/PVA coating with "bricks and mortar" structure effectively blocks the permeation of electrolyte due to the reduced porosity and enhanced densification. The corrosion rate of Ce(IV)/GO/PVA coating is 11 and 19 times lower than bare Mg alloy and single GO/PVA film, respectively. The wear rate of GO/PVA and Ce(IV)/GO/PVA samples is decreased by 98.8% and 97.6%, which is ascribed to the high hardness and lubrication of GO sheets. Moreover, the relatively interlayer slipping between GO sheets can lubricate the sliding process. Compared with GO/PVA, the slightly decreased wear resistance of Ce(IV)/GO/PVA coating is resulted from the enhanced shear force. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Strain-controlled magnetic ordering in 2D carbon metamaterials
    We use ab initio spin-polarized density functional theory to study the magnetic order in a Kagome-like 2D metamaterial consisting of pristine or substitutionally doped phenalenyl radicals polymerized into a nanoporous, graphene-like structure. In this and in a larger class of related structures, the constituent polyaromatic hydrocarbon molecules can be considered as quantum dots that may carry a net magnetic moment. The structure of this porous system and the coupling between the quantum dots may be changed significantly by applying moderate strain, thus allowing to control the magnetic order and the underlying electronic structure. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Insights into mesoporous nitrogen-rich carbon induced synergy for the selective synthesis of ethanol
    This work provides an in-depth study on selective ethanol synthesis over cobalt and copper supported on mesoporous nitrogen-rich carbon (MCN) materials. A series of nano-sized Cu-Co@MCN catalysts with variable compositions were designed to maximize the ethanol yield from bio-derived syngas (CO/H-2 > 2) by utilizing a nitrogen-rich mesoporous carbon (MCN), which serves two purposes i) the stabilisation of relatively small sized Co nanoparticle crystallites (Co: below 10 nm, geometrical structural promoter) with strong metal support interactions and ii) the promotion of sufficient electronic interactions (electronic promoter) to improve the reducibility of the catalyst. Characterisation of these novel catalysts by a range of techniques (XRD, BET, TPR, HRTEM, XPS, and EXAFS) confirmed that the metal ions are confined within the MCN matrix with highly uniform dispersion. This enhances metal support interactions, which promotes associative CO adsorption over complete CO dissociation. The Cu-Co@MCN catalyst shows potential for higher alcohol synthesis with high product selectivity for C1-C3 oxygenates in the liquid product stream, making it an attractive solution to alternative synthesis of higher alcohols. To elucidate the actual role of surface support nitrogen in-situ synchrotron PXRD studies were performed on the catalyst systems as well as on traditional support alternatives, e.g., carbon nanotubes and activated carbon. Furthermore, insights on catalyst deactivation and selectivity were achieved by in-situ high temperature infrared spectroscopic analysis (DRIFTS) studies, which is followed by in-depth Density Functional Theory (DFT) calculations outline the plausible route via stabilisation of CHO*, CH2O* intermediates for selective ethanol formation. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Sintered Fe/CNT framework catalysts for CO2 hydrogenation into hydrocarbons
    Because of its contribution to greenhouse effect, carbon dioxide conversion to valuable chemicals is one of the most challenging issues facing the modern world. A new type of iron catalysts of CO2 hydrogenation into hydrocarbons was synthesized by spark plasma sintering of carbon nanotubes decorated with iron oxide nanoparticles. This treatment produced carbon-encapsulated iron nanocrystals embedded in a dense framework of CNTs. The sintered catalysts were tested without pre-reduction in CO2 hydrogenation under supercritical conditions (350 degrees C, 8.5 MPa) and showed high specific activities of 5.4-12.2 mol(CO2)g(Fe)(-1)s(-1) and promising C2+ selectivities of 40-50 mol.% at rather low H-2:CO2 ratios of 1 and 2. The high efficiency of the catalysts was attributed to the stabilization of metal nanoparticles by carbon shells and increased density of CNT support, which led to higher degree of metal - support interaction and intensified carbidization and CO activation. (C) 2020 Elsevier Ltd. All rights reserved.
  • [期刊] Novel high-k gate dielectric properties of ultrathin hydrocarbon films for next-generation metal-insulator-semiconductor devices
    New high-k gate dielectrics are highly necessary in facilitating the continuous down-scaling of metal -oxide-semiconductor devices to the sub-10 nm range. This study presents ultrathin organic hydrocarbon (HC) films as a novel high-k gate insulator for metal-insulator-semiconductor (MIS) devices. During inductively-coupled plasma chemical vapor deposition with CH4 and H-2 gases, the growth temperature greatly affects the structure of the carbon layers and consequently their dielectric characteristics. Specifically, sp(2)-rich dielectric HC layers are formed below 600 degrees C, whereas highly-ordered sp(2)-hybridized graphene is formed at 950 degrees C. The k value of the resulting HC films increases up to a maximum value of 90 at 350 degrees C. Moreover, the MIS devices exhibit excellent gate-insulating properties, including almost no hysteresis in the capacitance-voltage curve, low leakage current, and high dielectric strength, which surpass those of existing high-k gate oxides. These results reveal that the organic HC films are a promising next-generation high-k gate dielectric material for sub-10 nm node Si and organic semiconductor technologies. (C) 2019 Elsevier Ltd. All rights reserved.
意见反馈
返回顶部