Graphene-based Metal Research Articles

"Butterfly effect" in CuO/graphene composite nanosheets: a small interfacial adjustment triggers big changes in electronic structure and Li-ion storage performance.

Generally speaking, excellent electrochemical performance of metal oxide/graphene nanosheets (GNSs) composite is attributed to the interfacial interaction (or "synergistic effect") between constituents. However, there are no any direct observations on how the electronic structure is changed and how the properties of Li-ion storage are affected by adjusting the interfacial interaction, despite of limited investigations on the possible nature of binding between GNSs and metal oxide. In this paper, CuO nanosheets/GNSs composites with a little Cu2O (ca. 4 wt %) were utilized as an interesting model to illustrate directly the changes of interfacial nature as well as its deep influence on the electronic structure and Li-ion storage performance of composite. The interfacial adjustment was successfully fulfilled by removal of Cu2O in the composite by NH3·H2O. Formation of Cu-O-C bonds on interfaces both between CuO and GNSs, and Cu2O and GNSs in the original CuO/GNSs composites was detected. The small interfacial alteration by removal of the little Cu2O results in the obvious changes in electronic structure, such as weakening of covalent Cu-O-C interfacial interaction and recovery of π bonds in graphene, and simultaneously leads to variations in electrochemical performance of composites, including a 21% increase of reversible capacity, degradation of cyclic stability and rate-performance, and obvious increase of charge-transfer resistance, which can be called a "butterfly effect" in graphene-based metal oxide composites. These interesting phenomena could be helpful to design not only the high-performance graphene/metal oxide anode materials but also various advanced graphene-based composites used in the other fields such as sensors, catalysis, fuel cells, solar cells, etc.

Graphene-based metal oxide nanocomposites and their application as adsorbents in water treatment schemes

Owing to their remarkable physicochemical properties, such as two-dimensional (2D) layer structures, large surface areas, pore volumes, and surface functional groups, graphene and graphene oxide materials have great potential in water treatment related applications. Graphene and graphene oxide sheets serving as 2D substrates can effectively inhibit aggregation of metal oxide nanoparticles and enable good nanoparticle dispersion. In this review, we discuss recent developments and achievements in the use of metal oxide-graphene composites for water purification. We also provide a comprehensive analysis of the nature of the interaction between such composites and various types of pollutants during adsorption processes, and discuss future challenges and applications.

Metal Deposition on Graphene Layers and Electrochemical Measurements at Liquid/Liquid Interface: Preparation of Graphene-Based Metal Nanostructures

Polarisable liquid/liquid interfaces have been investigated for over 30 years, mainly in the context of ion and electron transfer reactions. Electrical polarisation of the interface between two immiscible electrolyte solutions (ITIES) generates electrochemical potential gradients capable of promoting ion and electron transfer across the molecular boundary. The potential drop across the liquid/liquid boundary is developed over a region of 1 to 10 nm. The nucleation of metallic structures, catalytic activity e.g. hydrogen and oxygen evolution, the assembly of nanoparticles or catalytic nanoparticles have received a great interest in the last years.1-2 Graphene nanomaterials were prepared in two ways: gravity exfoliation from natural graphite in 1,2-dichloroethane (DCE) dispersion and chemical vapor deposition (CVD) on copper foil. Both types of material were assembled at the interface between two immiscible electrolyte solutions. The graphene materials before and after assembly were characterized by Atomic Force Microscopy (AFM) and Raman spectroscopy. The electrochemical reactivity of assembled graphene materials was probed by model redox species at the ITIES. In situ electrochemical and spontaneous metal deposition of palladium, gold and silver at the interface assembled carbon nanomaterials were studied. The identification and morphology of the deposited metal was determined using electron microscopy. The 2D graphene-based metal nanostructures effects were studied for the model redox species process at the ITIES.The graphene-metal composites preparation procedure at the ITIES opens an alternative way to prepare catalyst materials. Deeper understanding of the behavior of model redox couples on graphene is of primary importance in the exploitation of this material in catalytic processes, such as of the oxidation of low molecular weight alkanes to liquid fuels.1. Fermin, D. J.; Ding, Z.; Duong, H. D.; Brevet, P. F.; Girault, H. H., Journal of Physical Chemistry B, 1998, 102, 10334-10341.2. Dryfe, R. A. W., Physical Chemistry Chemical Physics, 2006, 8, 1869-1883.

Supercritical Deposition Route of Preparing Pt/Graphene Composites and Their Catalytic Performance toward Methanol Electrooxidation

The production of effective loading and direct deposition of Pt nanoparticles on graphene is difficult because this intriguing carbon material has highly hydrophobic surface properties. In this work, Pt/graphene sheet (GS) composites were successfully synthesized via a simple, effective, and environmentally benign one-pot supercritical carbon dioxide deposition route using dimethyl (1,5-cyclooctadiene) platinum(II) (PtMe2COD) as a soluble organometallic precursor. The preparation process obviates the need for solvents, which are often volatile and toxic. No post-treatment processes such as washing and drying are needed. Transmission electron microscopy shows that ultrafine metal nanoparticles with an average size as small as ∼2 nm are densely and evenly decorated on the hydrophobic surfaces of GS at Pt loadings up to 80 wt %. Electrochemical studies reveal that the prepared Pt/GS composites possess notably higher catalytic activity and better stability toward methanol electrooxidation in comparison with Pt/multiwalled carbon nanotube and Pt/carbon black composites. The supercritical carbon dioxide deposition method could be easily extended to the fabrication of other graphene-based metal composites with desirable properties by selecting suitable organometallic precursors.

Fabrication of Co3O4/graphene oxide composites using supercritical fluid and their catalytic application for the decomposition of ammonium perchlorate

We report a facile and environmentally benign approach to fabricate Co3O4 nanoparticles (NPs)/graphene oxide (G-O) composites by the use of supercritical fluid. With the aid of supercritical carbon dioxide, the ultrafine Co3O4 NPs are densely and homogeneously deposited on the supporting G-O sheets. Transmission electron microscope images revealed that the average size of Co3O4 NPs in Co3O4/G-O composites was 5.9 nm, much smaller than that of bare Co3O4 NPs, indicating that the graphene oxide sheets with Co3O4 NPs attached could hinder the growth and aggregation of Co3O4 crystals during synthesis. The layered graphite oxide sheets are exfoliated by the nucleation and growth of Co3O4 NPs. The composites exhibit a special catalytic effect for the thermal decomposition of ammonium perchlorate due to the combination of G-O sheets and Co3O4 NPs. This supercritical fluid method could be further extended to synthesize other G-O or graphene-based metal oxide composites using appropriate metal precursors.

Ultrathin MoS2/Nitrogen‐Doped Graphene Nanosheets with Highly Reversible Lithium Storage

The extensive range of possibilities for using a rechargeable lithium ion battery (LIB) for stationary power storage applications has stimulated signifi cant research to improve its energy, power density and cycling life. The current use of graphite as a commercially available anode material cannot fully meet the energy density requirements for LIB applications in electric vehicles due to its relatively small capacity (372 mAh/g). In the next generation LIB, graphite should be replaced by alternative higher capacity materials and graphene based composite is one of the promising choices. The discovery of graphene has attracted wide-ranging interest due to its unique physical and chemical properties and potential for applications in electronic devices and sensors. [ 1–3 ] This has led to the development of a signifi cant number of graphene-based materials for use as LIB anodes and results have been generally promising due to high specifi c capacity and improvement of its cycling ability. In recent years, chemical substitutional doping has been used to enhance the properties of graphene—further improving its properties beyond just morphology and size control. This includes the use of sulfur, boron, and nitrogen doping, the latter of which is particularly effective in modulating the electronic properties of graphene. [ 4–6 ] Based on these results, we expect that nitrogen-doped (N-doped) graphene will be used as a template for synthesis of active electrode materials. Compared to graphene-based metal oxide materials, some graphene-based transition metal sulfi des possess consummate 2D-layered structures. The matched structure between transition metal sulfi des and graphene avoids the exfoliation of electrode materials and capacity fading during the charge/discharge process. [ 7–9 ] As a typical layered transition metal sulfi de, MoS 2 has a structure similar to graphite, consisting of three atom layers of S-Mo-S stacked together through van der Waals interactions. [ 10 , 11 ] This layered structure enables the effi cient intercalation and deintercalation of lithium ions. In recent years, many published reports have articulated various processes for preparing MoS 2 or MoS 2 composites as LIB anodes, which

Synthesis of three-dimensional reduced graphene oxide layer supported cobalt nanocrystals and their high catalytic activity in F–T CO2 hydrogenation

The reduced graphene oxide (rGO) supported cobalt nanocrystals have been synthesized through an in situ crystal growth method using Co(acac)2 under solvothermal conditions by using DMF as the solvent. By carefully controlling the reaction temperature, the phase transition of the cobalt nanocrystals from the cubic phase to the hexagonal phase has been achieved. Moreover, the microscopic structure and morphology as well as the reduction process of the composite have been investigated in detail. It is found that oxygen-containing functional groups on the graphene oxide (GO) can greatly influence the formation process of the Co nanocrystals by binding the Co(2+) cations dissociated from the Co(acac)2 in the initial reaction solution at 220 °C, leading to the 3D reticular structure of the composite. Furthermore, this is the first attempt to use a Co/rGO composite as the catalyst in the F-T CO2 hydrogenation process. The catalysis testing results reveal that the as-synthesized 3D structured composite exhibits ideal catalytic activity and good stability, which may greatly extend the scope of applications for this kind of graphene-based metal hybrid material.

Sandwich-structural graphene-based metal oxides as anode materials for lithium-ion batteries

Graphene-based metal oxides commonly show outstanding electrochemical performance due to the superior properties of graphene. However, the as-formed metal oxides decorated on graphene prefer to disintegrate or aggregate together, and the graphene–metal oxide hybrids also randomly aggregate themselves, resulting in capacity fading and poor cycling stability. Herein, the graphene-based metal oxides are further protected by graphene nanosheets through a stepwise heterocoagulation method, producing a layered sandwich structure. Compared to the normal graphene-based metal oxides, the sandwich-like graphene-based composites exhibit higher reversible capacities, better cycle performances, and higher rate capabilities. Such sandwich structure can avoid the aggregation of the composites and also act as an ideal strain buffer to alleviate the volume change of metal oxides during cycles. Moreover, the electronic conductivity of the electrode can be further enhanced by the introduction of additional graphene nanosheets. This double layer protection strategy is very effective and may be extended to prepare other high-capacity electrode materials for lithium-ion batteries.

α-Fe2O3 nanoparticles anchored on graphene with 3D quasi-laminated architecture: in situ wet chemistry synthesis and enhanced electrochemical performance for lithium ion batteries

A novel α-Fe2O3/graphene composite is prepared by a simple in situ wet chemistry approach. The α-Fe2O3 particles with diameter around 130 nm are homogeneously anchored on graphene nanosheets to form a 3D quasi-laminated architecture. Such a well-organized flexible structure can offer sufficient void space to facilitate the electrolyte penetration, alleviate the effect of the volume change of α-Fe2O3 particles and avoid particle–particle aggregation during lithium insertion/desertion. In addition, graphene not only improves the electric conductivity of the composite electrode but also maintains the structural integrity of the composite electrode during long-term cycling. As anode material for Li-ion batteries, the α-Fe2O3/graphene composite electrode exhibits a stable capacity of 742 mAh g−1 up to 50 cycles. The synthesis technique is suitable for practical large-scale production of graphene-based metal oxide composites as advanced electrode materials for rechargeable Li-ion batteries.

Facile and rapid synthesis of RGO–In2S3 composites with enhanced cyclability and high capacity for lithium storage

A sheet-on-sheet reduced graphene oxide-β-In(2)S(3) (RGO-In(2)S(3)) composite, was successfully synthesized via a one-step mild method. This fresh composite used as an anode material exhibits enhanced cyclability and specific capacity for lithium storage. These results are linked with the intrinsic layered structure of β-In(2)S(3) sheets and the effective combination of β-In(2)S(3) and RGO sheets. This results in a high specific surface area and good conductivity of RGO-In(2)S(3) composites, with higher transport rates of electrolyte ions and electrons, and a more effective electrochemical reaction of the active material. This facile and rapid synthesis method is a promising route for a large-scale production of graphene-based metal sulfides, which could be used as electrode materials for Li-ion batteries.

Reversible phase transfer of graphene oxide and its use in the synthesis of graphene-based hybrid materials

A phase transfer protocol for graphene oxide (GO) was demonstrated with a long chain alkylamine–dodecylamine (DDA) as phase transfer agent. By this method, GO sheets can be easily transferred from water to various low polar organic solvents such as cyclohexane, petroleum ether, kerosene, toluene, carbon tetrachloride, etc. through forming noncovalent DDA–GO hybrids. The reversible phase transfer of GO between aqueous phase and organic phase was also realized through the formation and destruction of a DDA–GO micelle. It was found that ethanol plays a critical role in the phase transfer process, while other experimental parameters, such as pH value and the concentration of GO, do not have an obvious influence on the transfer efficiency over a wide range. A detailed mechanism for the phase transfer is proposed on the basis of experimental observation. With this phase transfer technique, a simple, efficient, and versatile approach is also developed to synthesize a variety of graphene-based metal and alloy hybrids in low-polar organic solvents.