Reduced graphene oxide supported highly porous V2O5 spheres as a high-power cathode material for lithium ion batteries

Reduced graphene oxide (rGO) supported highly porous polycrystalline V(2)O(5) spheres (V(2)O(5)/rGO) were prepared by using a solvothermal approach followed by an annealing process. Initially, reduced vanadium oxide (rVO) nanoparticles with sizes in the range of 10-50 nm were formed through heterogeneous nucleation on rGO sheets during the solvothermal process. These rVO nanoparticles were oxidized to V(2)O(5) after the annealing process in air at 350 °C and assembled into polycrystalline porous spheres with sizes of 200-800 nm. The weight ratio between the rGO and V(2)O(5) is tunable by changing the weight ratio of the precursors, which in turn affects the morphology of V(2)O(5)/rGO composites. The V(2)O(5)/rGO composites display superior cathode performances with highly reversible specific capacities, good cycling stabilities and excellent rate capabilities (e.g. 102 mA h g(-1) at 19 C).     

Synthesis and characterization of graphene–nickel oxide nanostructures for fast charge–discharge application

Graphene–metal oxide composites as anode materials for Li-ion batteries have been investigated extensively, but these attempts are mostly limited to moderate rate charge–discharge applications. Here, graphene–nickel oxide nanostructures have been synthesised using a controlled hydrothermal method, which enabled in situ formation of NiO with a coralloid nanostructure on graphene. Graphene/NiO (20%), graphene/NiO (50%) and pure NiO show stable discharge capacities of 185 mAh/g at 20 C (1 C = 300 mA/g), 450 mAh/g at 1 C, and 400 mAh/g at 1 C, respectively. High rate capability and good stability in prolonged charge–discharge cycling permit the application of the material in fast charging batteries for upcoming electric vehicles. To the best of our knowledge such fast rate performance of graphene/metal oxide composite as anode and such stability for pure NiO as anode have not been reported previously.     

Controlled assembly of Fe3O4 magnetic nanoparticles on graphene oxide

We describe a facile approach to controllable assembly of monodisperse Fe(3)O(4) nanoparticles (NPs) on chemically reduced graphene oxide (rGO). First, reduction and functionalization of GO by polyetheylenimine (PEI) were achieved simultaneously by simply heating the PEI and GO mixture at 60 °C for 12 h. The process is environmentally friendly and convenient compared with previously reported methods. Meso-2,3-dimercaptosuccinnic acid (DMSA)-modified Fe(3)O(4) NPs were then conjugated to the PEI moiety which is located on the periphery of the GO sheets via formation of amide bonds between COOH groups of DMSA molecules bound on the surface of the Fe(3)O(4) NPs and amine groups of PEI. The magnetic GO composites were characterized by means of TEM, AFM, UV-vis, FTIR, Raman, TGA, and VSM measurements. Finally, preliminary results of using the Fe(3)O(4)-rGO composites for efficient removal of tetracycline, an antibiotic that is often found as a contaminant in the environment, are reported.     

基于β-FeOOH纳米棒制备LiFePO_4/C和Fe_2O_3纳米电极材料及其电池性能

自制直径为90nm、长为500nm的β-FeOOH纳米棒为前驱物,通过碳热还原法和热分解法分别制备出形貌均匀、粒径为300nm的LiFePO4/C正极材料和粒径为100nm的Fe2O3负极材料,并研究它们对金属锂组成半电池和构造LiFePO4/C vs.Fe2O3全电池的电化学性能。结果表明：LiFePO4/C半电池在0.1C、0.5C、1.0C、5.0C、10.0C和15.0C（1C=170 mA g–1）倍率下放电比容量分别为158.8、153.2、144.3、126.8、111.0 mA h g–1和92.9mA h g–1。经过不同倍率循环后,返回0.1 C放电比容量为157.5mA h g–1,为初始0.1 C放电比容量的99.2%。Fe2O3半电池在50mA g–1电流密度下首次放电比容量为1655.5mA h g–1,循环50次后,仍保持460mA h g–1的放电比容量。LiFePO4/C vs.Fe2O3全电池在0.1 C倍率下,相对于LiFePO4活性物质,首次放电比容量为148.7mA h g–1;相对于Fe2O3活性物质,首次放电比容量为441.7mA h g–1。由LiFePO4/C纳米粒子作为正极材料、Fe2O3纳米粒子作为负极材料组成的全电池在0.1 C到2.0 C不同倍率下均表现出了良好的循环性能,且返回0.1 C后其放电比容量相对于初始0.1 C放电比容量无衰减。可见,以β-FeOOH纳米棒为前驱物控制制备的LiFePO4/C正极纳米材料和Fe2O3负极纳米材料可以有效地提升电池的性能。     

CoO/rGO composite prepared by a facile direct-flame approach for high-power supercapacitors

In this study, CoO nanoparticles (NPs) measuring approximately 20?nm in size are successfully grown on reduced graphene oxide (rGO) layers through a facile direct-flame approach. The obtained CoO/rGO nanocomposites are applied as electrode materials and show a high specific capacitance, reaching 1615.0?F?g^?1 at a current of 1?A?g^?1 (737.5?F?g^?1 at 50?A?g^?1), and good cycling stability (88.12% retention after more than 15,000 cycles at 5?A?g^?1), which are outstanding characteristics compared with those of recently reported pseudosupercapacitors. Furthermore, an asymmetric supercapacitor (ASC) produced using CoO/rGO as a positive electrode material and activated graphene (AG) as a negative electrode achieves a high cell voltage of 1.6?V and delivers a maximum energy density of 62.46?Wh?kg^?1 at a power density of 1600?W?kg^?1. The fabrication technique is facile and represents a promising means of obtaining metal oxide/graphene composites for high-performance supercapacitors.     

Graphene-supported cubic hollow carbon shell-coated germanium particles as high-performance anode for lithium-ion batteries

Germanium-based materials are considered to be an alternative material for high energy density lithium-ion battery anodes due to their superior theoretical capacity. However, the severe volume expansion during the lithium insertion and the easily agglomerated tendency of Ge nanoparticles become the key obstacles to the stable cycle and capacity retention of Ge anodes. Herein, we designed a double-layered protective structure in which the cubic hollow Ge@C hybrids are uniformly dispersed on reduced graphene oxide sheets (Ge@C-rGO) through conventional dopamine-coated precursor and subsequent carbothermal reduction processes. In the synthesized Ge@C-rGO hybrids, the large-area rGO sheets cooperate with the amorphous carbon layer to accommodate and buffer the volume expansion of Ge particles, and to ensure that the Ge nanoparticles are in a separated state to the utmost extent. The Ge@C-rGO electrode which is employed in lithium-ion battery owns the reversible capacities of 1183 mAh·g⁻¹ at the specific current of 100 mA g⁻¹ and 710 mAh·g⁻¹ at 1 A g⁻¹ for 200 cycles. In addition, it exhibited good cycle stability, rate reversibility and electronic conductivity, and is a potential anode material with high performance and long-cycle capability.     

Reduced graphene oxide for Li–air batteries: The effect of oxidation time and reduction conditions for graphene oxide

Reduced graphene oxide (rGO) has shown great promise as an air-cathode for Li–air batteries with high capacity. In this article we demonstrate how the oxidation time of graphene oxide (GO) affects the ratio of different functional groups and how trends of these in GO are extended to chemically and thermally reduced GO. We investigate how differences in functional groups and synthesis may affect the performance of Li–O₂ batteries. The oxidation timescale of the GO was varied between 30 min and 3 days before reduction. Powder X-ray diffraction, micro-Raman, FE-SEM, BET analysis, and XPS were used to characterize the GO’s and rGO’s. Selected samples of GO and rGO were analyzed by solid state ¹³C MAS NMR. These methods highlighted the difference between the two types of rGO’s, and XPS indicated how the chemical trends in GO are extended to rGO. A comparison between XPS and ¹³C MAS NMR showed that both techniques can enhance the structural understanding of rGO. Different rGO cathodes were tested in Li–O₂ batteries which revealed a difference in overpotentials and discharge capacities for the different rGO’s. We report the highest Li–O₂ battery discharge capacity recorded of approximately 60,000 mAh/g_carbon achieved with a thermally reduced GO cathode.     

Nano-sized cobalt oxide/mesoporous carbon sphere composites as negative electrode material for lithium-ion batteries

A new type of nano-sized cobalt oxide compounded with mesoporous carbon spheres (MCS) as negative electrode material for lithium-ion batteries was synthesized. The composite containing about 20 wt.% cobalt oxide exhibits a reversible capacity of 703 mAh/g at a constant current density of 70 mA/g between 0.01 and 3.0 V (vs. Li⁺/Li), and remains a capacity retention of 77% after the 30th cycle. The improvement could be attributed to that the MCS had a good electronic conductivity and severed as dispersing medium to prevent cobalt oxide nanoparticles from aggregating, and the mesopores (cobalt oxide not fully occupied) can provide the enough space to buffer the volume change during the Li-ion insertion and extraction reactions in cobalt oxide nanoparticles.     

Nanocomposites of size-controlled gold nanoparticles and graphene oxide: formation and applications in SERS and catalysis

In this paper, we describe the formation of Au nanoparticle-graphene oxide (Au-GO) and -reduced GO (Au-rGO) composites by noncovalent attachment of Au nanoparticles premodified with 2-mercaptopyridine to GO and rGO sheets, respectively, viaπ-π stacking and other molecular interactions. Compared with in situ reduction of HAuCl4 on the surface of graphene sheets that are widely used to prepare Au-GO composites, the approach developed by us offers well controlled size, size distribution, and morphology of the metal nanoparticles in the metal-GO nanohybrids. Moreover, we investigated surface enhanced Raman scattering (SERS) and catalysis properties of the Au-graphene composites. We have demonstrated that the Au-GO composites are superior SERS substrates to the Au NPs. Similarly, a comparative study on the catalytic activities of the Au, Au-GO, and Au-rGO composites in the reduction of o-nitroaniline to 1,2-benzenediamine by NaBH4 indicates that both Au-GO and Au-rGO composites exhibit significantly higher catalytic activities than the corresponding Au nanoparticles.     

Synthesis of MnOx/reduced graphene oxide nanocomposite as an anode electrode for lithium-ion batteries

We report the high performance of the manganese oxide/reduced graphene oxide (MnOx/rGO) nanocomposite as an anode electrode of a lithium-ion battery. The composite is synthesized by a low temperature (83 °C) chemical solution reaction, and shows relatively high specific capacities (660 mAh g⁻¹) after 50 cycles. For MnOx/rGO composites, the cycling stability is increased remarkably as compared to that seen with individual MnOx, and this is due to the synergistic effects of both the components in the composite. The rGO acts as a conductive buffer layer that suppresses the volume change of MnOx, and simultaneously promotes the conductivity of MnOx. The functional groups of graphene oxide facilitate MnOx formation at low temperature, and this retains the MnOx-graphene oxide connection, thus improving the capacity and cycling stability.     

Li0.95Na0.05MnPO4/C nanoparticles compounded with reduced graphene oxide sheets for superior lithium ion battery cathode performance

Sodium-substituted LiMnPO₄/C/reduced graphene oxide (LNMP@rGO) was synthesized in this study via freeze drying and carbon thermal reduction method with graphene oxide as carbon source. Sodium ion doping is optimized and rGO effects are evaluated by XRD, SEM, TEM, BET, Raman, and electrochemical performance measurements. Well-distributed nanoparticles with average size of ~50?nm are evenly distributed on the surface or intercalation between rGO layers, resulting in a porous ion/electronic conductive network. Compared to 122.3?mA?h?g^?1 in unmodified LNMP, the best LNMP@rGO (20?mg rGO) exhibits an excellent initial discharge capacity of 150.4?mA?h?g^?1 at 0.05?C at 122.9% of the initial capacity. The capacity retention rate is 95.8% of the initial capacity after 100 cycles at 1?C. Capacity of 101.2?mA?h?g^?1 is preserved even at rates as high as 10?C.     

Preparation and electrochemical properties of polyaniline/reduced graphene oxide composites

Polyaniline (PANI)/reduced graphene oxide (rGO) composites were synthesized by in situ oxidative polymerization of aniline on reduced graphene sheets. Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, transmission electron microscopy, and scanning electron microscopy were used to characterize the composites. The results indicated PANI/rGO composites were produced and contained covalent bonds between the functional groups of PANI and rGO. A uniform coating of PANI on the rGO sheets had a synergistic effect on the properties of the composites. The electrochemical properties of the PANI/rGO composites produced using different feed ratios of aniline to rGO were studied. The results showed that the composites exhibited a maximum specific capacitance of 797.5 F/g at 0.5 A/g and minimum charge transfer resistance of 0.98 Ω when the feed ratio of aniline to rGO was 2:1. These values were superior to those of pure PANI and rGO. The composites also displayed excellent cycling stability, with specific capacitance retention of 92.43% after 1000 cycles. These stable structural composites show promise for the development of new supercapacitor applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46103.     

Iron oxide supercapacitor of high volumetric energy and power density using binder-free supersonic spraying and self-healing rGO

Iron oxide (Fe₂O₃) nanoparticles and reduced graphene oxide (rGO) sheets were supersonically sprayed onto a nickel substrate to fabricate flexible supercapacitors. The supersonic impact velocity was adjusted by varying the air chamber pressure from 2 to 6 bar, which facilitated the self-healing of Stone-Wall defects in rGO sheets. Supersonic spraying caused exfoliation of the rGO sheets, which in turn increased the surface area and adherence of the Fe₂O₃ nanoparticles. The optimal case exhibited a specific capacitance of 1.44 F?cm^-2 at a current rate of 1.5 mA?cm^-2 and the energy density was 14.23 mWh?cm^-3 at 250 mW?cm^-3. The width of the potential window increased to 1.4 V, implying a significant increase in the energy storage capability. The energy density of the supersonically sprayed Fe₂O₃/rGO electrode also showed no signs of deterioration even when the increased current density interfered with the electrode performance.     

Effect of annealing temperature and graphene concentrations on photovoltaic and NIR-detector applications of PbS/rGO nanocomposites

The effect of annealing temperature on photovoltaic and near-infrared (NIR) detector applications of PbS nanoparticles (NPs) and PbS/graphene nanocomposites was investigated. The products were synthesized by a simple co-precipitation method and graphene oxide (GO) sheets were used as graphene source. Several characterization techniques were used to show transfer of the GO into reduced graphene oxide (rGO) during the synthesis process. In addition, the effect of graphene concentrations on morphology, structure, photovoltaic, and detector parameters of the samples were studied. Transmission electron microscope (TEM) images showed that, the PbS NPs were agglomerated, while, the PbS/rGO nanocomposites were dispersed completely after annealing under H₂/Ar gas atmosphere. UV–visible spectrometer showed an absorption peak for all samples in the near infrared red (NIR) region of the electromagnetic spectrum. The results indicated that, photocurrent intensity, responsivity of the samples to an NIR source, and solar-cell efficiency were affected by annealing of samples and graphene concentrations.     

Hydrothermal synthesis of Ag2CO3-TiO2 loaded reduced graphene oxide nanocomposites with highly efficient photocatalytic activity

Abstract

In this work, a growth of Ag₂CO₃-TiO₂ NPs over GO sheets and reduction of GO were simultaneously achieved by the hydrothermal process at 130 °C for 4?h. The photocatalytic activity of the as-prepared Ag₂CO₃-TiO₂ NPs decorated reduced graphene oxide (Ag₂CO₃-TiO₂/rGO) composite was studied by the degradation of methylene blue (MB) solution under visible light irradiation. A remarkable enhancement in the photocatalytic activity of the TiO₂ was achieved after sensitizing with Ag₂CO₃ and loading in rGO sheets which is attributed to the reduced charge recombination, enhanced dye adsorption, and the improvement in the light harvesting capacity of the composite.     

Reduced-graphene-oxide-reinforced boron carbide ceramics fabricated by spark plasma sintering from powder mixtures obtained by heterogeneous co-precipitation

Reduced graphene oxide (rGO) sheets were uniformly dispersed in boron carbide ceramics by a heterogeneous co-precipitation method. This approach was used to improve the fracture toughness of boron carbide ceramics and to address the problem of agglomeration of graphene in the boron carbide matrix. Cetyltrimethyl ammonium bromide was used as a heterogeneous co-precipitation reaction initiator to prepare a homogeneously dispersed graphene oxide/boron carbide (GO/B₄C) mixture. Reduced graphene oxide/boron carbide (rGO/B₄C) powder mixtures with good dispersion were obtained by high temperature heat treatment. Dense rGO/B₄C composite ceramics were fabricated by spark plasma sintering at 1800 °C and 50 MPa. The fracture toughness and flexural strength of the rGO/B₄C with an rGO content of 2 vol% composite increased by 42% (from 3.43 to 4.88 MPa·m^1/2) and 28% (from 372 to 476 MPa) compared with those of pure B₄C, respectively. The markedly improved fracture toughness and flexural strength of the boron carbide ceramics were attributed to the effect of crack bridging and crack deflection by graphene sheets, graphene interface sliding, and pulling out of graphene.     

Photovoltaic and UV detector applications of ZnS/rGO nanocomposites synthesized by a green method

The effect of graphene concentration on the photovoltaic and UV detector applications of ZnS/graphene nanocomposites was investigated. The nanocomposites were synthesized by a green, cost-effective, and simple co-precipitation method with different graphene concentrations (5, 10, and 15 wt%) using L-cysteine amino acid as a surfactant and graphene oxide (GO) powder as a graphene source. Transmission electron microscopy (TEM) images showed that the ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in ZnS diameter size. The results of X-ray diffraction (XRD) patterns, Raman, and Fourier transform infrared (FTIR) spectroscopy indicated that the GO sheets were changed into reduced graphene oxide (rGO) during synthesis process. Therefore, L-cysteine amino acid played its role as a reducing agent to reduce the GO. Photovoltaic measurements showed that the graphene caused to increase the efficiency of solar-cell application of ZnS/rGO nanocomposites. In addition, our observation showed that the nanocomposites were suitable as ultraviolet (UV) detectors and graphene concentration increased the responsibility of the detectors.     

Layer-by-layer assembled MoO₂-graphene thin film as a high-capacity and binder-free anode for lithium-ion batteries

Thin films of MoO(2) nanoparticles and graphene sheets are created by layer-by-layer (LBL) assembly as binder-free anodes for lithium-ion batteries. Both anionic polyoxometalate clusters and graphene oxide nanosheets with oxygen functional groups on both basal planes and edges are assembled into LBL films with the aid of a cationic polyelectrolyte. After a subsequent thermal treatment in an Ar-H(2) atmosphere, hybrid MoO(2)-graphene films with three-dimensionally interconnected nanopores are formed, which comprise ultrafine MoO(2) nanoparticles homogeneously embedded in the porous network of graphene nanosheets. When used as an anode for lithium-ion batteries, the MoO(2)-graphene thin-film electrode shows superior electrochemical performance with high specific capacity and excellent cyclability. A high specific capacity of 675.9 mA h g(-1) after 100 discharge-charge cycles is achieved, indicating a promising anode candidate for lithium-storage applications.     

Photochemical loading of metal nanoparticles on reduced graphene oxide sheets using phosphotungstate

Well-dispersed reduced graphene oxide (r-GO) sheets loaded with metal nanoparticles were produced in dimethylformamide (DMF). The r-GO suspension was prepared through the photocatalytic reduction of graphene oxide (GO) using a phosphotungstate as a homogeneous photocatalyst under UV irradiation. Immediately after UV lamp was turned off, the injection of precursors of Ag, Au, and Pd caused the rapid nucleation because photoreduced phosphotungstates as well as electrons stored in r-GO directly reduced metal ions. Furthermore, the r-GO sheets not only provided the nucleation sites but also prohibited the metal nanoparticles from agglomeration. As a result, relatively uniform-sized metal nanoparticles were formed on the r-GO sheets. With phosphotungstates and UV light irradiation, both GO and metal ions can be reduced to form the hybrids of Ag, Au, and Pd/r-GO as a suspension in DMF or an isolated paper sheet without using any toxic reagents.     

Biosensor based on Prussian blue nanocubes/reduced graphene oxide nanocomposite for detection of organophosphorus pesticides

We demonstrate a facile procedure to efficiently prepare Prussian blue nanocubes/reduced graphene oxide (PBNCs/rGO) nanocomposite by directly mixing Fe(3+) and [Fe(CN)(6)]((3)-) in the presence of GO in polyethyleneimine aqueous solution, resulting in a novel acetylcholinesterase (AChE) biosensor for detection of organophosphorus pesticides (OPs). The obtained nanocomposite was characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) microanalysis. It was clearly observed that the nanosheet has been decorated with cubic PB nanoparticles and nearly all the nanoparticles are distributed uniformly only on the surface of the reduced GO. No isolated PB nanoparticles were observed, indicating the strong interaction between PB nanocubes and the reduced GO and the formation of PBNCs/rGO nanocomposite. The obtained PBNCs/rGO based AChE biosensor make the peak potential shift negatively to 220 mV. The over-potential decreases ～460 mV compared to that on a bare electrode, suggesting that PBNCs/rGO has a high electrocatalytic activity towards the oxidation of thiocholine. The AChE biosensor shows rapid response and high sensitivity for detection of monocrotophos with a linear range from 1.0 to 600 ng mL(-1) and a detection limit of 0.1 ng mL(-1). These results suggest that the PBNCs/rGO hybrids nanocomposite exhibited high electrocatalytic activity towards the oxidation of thiocholine, which lead to the sensitive detection of OP pesticides.