Jinping Zhao

Graphene Anchored with Co3O4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance

We report a facile strategy to synthesize the nanocomposite of Co(3)O(4) nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co(3)O(4) nanoparticles obtained are 10-30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co(3)O(4)/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co(3)O(4) nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

Graphene Anchored with Co 3 O 4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance

We report a facile strategy to synthesize the nanocomposite of Co(3)O(4) nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co(3)O(4) nanoparticles obtained are 10-30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co(3)O(4)/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co(3)O(4) nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

Fabrication of Graphene/Polyaniline Composite Paper via In Situ Anodic Electropolymerization for High- Performance Flexible Electrode

Freestanding and flexible graphene/polyaniline composite paper was prepared by an in situ anodic electropolymerization of polyaniline film on graphene paper. This graphene-based composite paper electrode, consisting of graphene/polyaniline composite sheets as building blocks, shows a favorable tensile strength of 12.6 MPa and a stable large electrochemical capacitance (233 F g(-1) and 135 F cm(-3) for gravimetric and volumetric capacitances), which outperforms many other currently available carbon-based flexible electrodes and is hence particularly promising for flexible supercapacitors.

Efficient Preparation of Large-Area Graphene Oxide Sheets for Transparent Conductive Films

Large-area sheets are highly desirable for fundamental research and technological applications of graphene. Here we introduce a modified chemical exfoliation technique to prepare large-area graphene oxide (GO) sheets. The maximum area of the GO sheets obtained can reach ∼40000 μm(2). We found that the GO area is strongly correlated with the C-O content of the graphite oxide, which enables the area of the synthesized GO sheets to be controlled. By simply changing oxidation conditions, GO sheets with an average area of ca. 100-300, ca. 1000-3000, and ∼7000 μm(2) were selectively synthesized. For transparent conductive film applications, thin GO films were fabricated by self-assembly on a liquid/air interface and reduced by HI acid. We found that the sheet resistance of the reduced GO (rGO) films decreases with increasing sheet area at the same transmittance because of the decrease in the number of intersheet tunneling barriers. The rGO film made from GO sheets with an average area of ∼7000 μm(2) shows a sheet resistance of 840 Ω/sq at 78% transmittance, which is much lower than that (19.1 kΩ/sq at 79% transmittance) of a rGO film made from small-area GO sheets of ca. 100-300 μm(2), and comparable to that of graphene films grown on Ni by chemical vapor deposition.

Synthesis of graphene sheets with high electrical conductivity and good thermal stability by hydrogen arc discharge exfoliation.

We developed a hydrogen arc discharge exfoliation method for the synthesis of graphene sheets (GSs) with excellent electrical conductivity and good thermal stability from graphite oxide (GO), in combination with solution-phase dispersion and centrifugation techniques. It was found that efficient exfoliation and considerable deoxygenation of GO, and defect elimination and healing of exfoliated graphite can be simultaneously achieved during the hydrogen arc discharge exfoliation process. The GSs obtained by hydrogen arc discharge exfoliation exhibit a high electrical conductivity of approximately 2 x 10(3) S/cm and high thermal stability with oxidization resistance temperature of 601 degrees C, which are much better than those prepared by argon arc discharge exfoliation (approximately 2 x 10(2) S/cm, 525 degrees C) and by conventional thermal exfoliation (approximately 80 S/cm, 507 degrees C) with the same starting GO. These results demonstrate that this hydrogen arc discharge exfoliation method is a good approach for the preparation of GSs with a good quality.

Graphene sponge for efficient and repeatable adsorption and desorption of water contaminations

Seeking highly-efficient, low-cost and robust methods to disinfect and decontaminate water from source to point-of-use is very much in demand. Here, we developed a new material, graphene sponge (GS), for water treatment, which was assembled with graphene oxide sheets by hydrothermal treatment with the assistance of thiourea. These GSs show a tunable pore structure and surface properties, and are mechanically strong. They show high adsorption ability for various water contaminations such as dyes, oils and many other organic solvents. The adsorption capacity of methylene blue and diesel oil in GSs can reach 184 mg g−1 and 129 g g−1, respectively. Moreover, the GSs can be repeatedly used by simple treatment without obvious structure and performance degradation. Additionally, we studied the relationship between the structure and contamination adsorption performance of GSs. It was found that the dye adsorption performance of GSs strongly depends on their surface charge concentration and specific surface area, but the oil adsorption capacity is mainly related to their specific surface area, indicating the different adsorption mechanism. These findings open up many possibilities for the use of graphene in water cleaning, including disinfection, decontamination, re-use, reclamation and desalination.

Efficient growth of high-quality graphene films on Cu foils by ambient pressure chemical vapor deposition

We developed an ambient pressure chemical vapor deposition (CVD) for rapid growth of high-quality graphene films on Cu foils. The quality and growth rate of graphene films are dramatically increased with decreasing H(2) concentration. Without the presence of H(2), continuous graphene films are obtained with a mean sheet resistance of < 350 Omega/sq and light transmittance of 96.3% at 550 nm. Because of the ambient pressure, rapid growth rate, absence of H(2) and readily available Cu foils, this CVD process enables inexpensive and high-throughput growth of high-quality graphene films

Facile Preparation of One-Dimensional Wrapping Structure: Graphene Nanoscroll-Wrapped of Fe3O4 Nanoparticles and Its Application for Lithium-Ion Battery

Graphene nanoscroll (GNS) is a spirally wrapped two-dimensional (2D) graphene sheet (GS) with a 1D tubular structure resembling that of a multiwalled carbon nanotube (MWCNT). GNS provide open structure at both ends and interlayer galleries that can be easily intercalated and adjusted, which show great potential applications in energy storage. Here we demonstrate a novel and simple strategy for the large-scale preparation of GNSs wrapping Fe3O4 nanoparticles (denoted as Fe3O4@GNSs) from graphene oxide (GO) sheets by cold quenching in liquid nitrogen. When a heated aqueous mixed suspension of GO sheets and Fe3O4 nanoparticles is immersed in liquid nitrogen, the in-situ wrapping of Fe3O4 nanoparticles with GNSs is easily realized. The structural conversion is closely correlated with the initial temperature of mixed suspension, the zeta potential of Fe3O4 nanoparticles and the immersion way. Remarkably, such hybrid structure provides the right combination of electrode properties for high-performance lithium-ion batteries. Compared with other wrapping structure, such 1D wrapping structure (GNSs wrapping) effectively limits the volume expansion of Fe3O4 nanoparticles during the cycling process, consequently, a high reversible capacity, good rate capability, and excellent cyclic stability are achieved with the material as anode for lithium storage. The results presented here may pave a way for the large-scale preparation of GNS-based materials in electrochemical energy storage applications.

Controllable synthesis of graphene nanoscroll-wrapped Fe3O4 nanoparticles and their lithium-ion battery performance

In this work, a series of graphene nanoscroll (GNS)-wrapped Fe3O4 nanoparticles (NPs) composites (denoted as Fe3O4@GNS) are prepared by cold quenching of mixed suspensions of water-dispersible Fe3O4 NPs and graphene oxide (GO) with different mass ratios in liquid nitrogen followed by a low-temperature thermal reduction. In all samples, it is interesting that Fe3O4 NPs are able to be in situ encapsulated completely in GNSs, forming a three-dimensional network consisting of a fiber-like structure. The amount of Fe3O4 NPs wrapped with GNSs is in proportion to the mass ratio between Fe3O4 NPs and GO in the initial mixed suspension. As a new anode material of lithium ions batteries (LIBs), these Fe3O4@GNSs exhibit outstanding Li-ion storage characteristics. Among them, the Fe3O4@GNS (Fe3O4 : GO = 2 : 1) electrode shows the best electrochemical properties, including excellent cycling stability with a reversible capacity of 1172 mA h g−1 over 200 cycles at 100 mA g−1 and 525 mA h g−1 over 1000 cycles at 2 A g−1, as well as superior rate performance with a reversible capacity of 648 and 480 mA h g−1 at 2 and 5 A g−1, respectively. Such high performance is very close to the novel hybrid structure of Fe3O4@GNS as well as the optimal ratio between Fe3O4 and GO.