Conductive Graphene Nanosheets Research Articles

Co0.85Se hollow nanospheres anchored on N-doped graphene nanosheets as highly efficient, nonprecious electrocatalyst for hydrogen evolution reaction in both acid and alkaline media

Developing nonprecious electrocatalysts with high efficiency in both acid and alkaline electrolytes is extremely important for realizing scalable water-splitting technology. Herein, for the first time, we present a facile and cost-effective hydrothermal approach to synthesize a novel hybrid electrocatalyst of Co0.85Se/nitrogen-doped graphene, where Co0.85Se hollow nanospheres are homogenously anchored on nitrogen-doped reduced graphene oxide nanosheets. This hybrid electrocatalyst delivers outstanding hydrogen evolution reaction performance with very low onset potentials of −159 and −111 mV, low overpotentials of −209 and −227 mV at 10 mA cm−2, and small Tafel slopes of 36.1 and 76.5 mV dec−1 in acid and alkaline electrolytes, respectively. Furthermore, it shows superior durability even after 1500 cycles. The excellent electrocatalytic performance of the Co0.85Se/nitrogen-doped graphene can be attributed to its well-designed nanoarchitecture. By anchoring Co0.85Se hollow nanospheres on highly conductive graphene nanosheets, the aggregation of Co0.85Se nanospheres is well suppressed, thus increasing the specific surface area and producing abundant exposed active sites. In addition, the charge transfer is greatly facilitated. The remarkable catalytic activity, long-term cycling stability and low-cost synthesis make Co0.85Se/nitrogen-doped graphene a desirable non-precious electrocatalyst for hydrogen evolution in both acid and alkaline electrolytes.

Dense graphene papers: Toward stable and recoverable Al-ion battery cathodes with high volumetric and areal energy and power density

Since Al ion batteries (AIBs) are known to be a novel energy storage prototype of more safe and higher energy density, challenges are still in the currently explored carbon cathodes, specifically in balancing the rapid ion transport channels and volumetric/areal energy storage capability at a dense fashion. In this contribution, exceptional graphene nanosheet (GN) papers that are well stacked by conductive graphene nanosheets have been demonstrated as an electrochemically stable host for fast AlCl4- ion transport/storage along with high volumetric/areal energy storage at a dense state (1.6~1.8gcm−3). Owing to the exclusive morphological and chemical advantages, the as-assembled AIBs with the binder-free GN paper cathode enables to deliver considerably high specific capacity 100mAhg−1 at the current density 50mAg−1 (approaching the theoretic value of carbon AIB cathodes), coupled with much enhanced volumetric capacity, areal energy density and power density compared to the reported carbon AIB cathodes. Particularly, the term of tortuosity has been employed to understand the fundamental relationship between volumetric energy performance and microscopic structures, which suggests a unique platform for developing advanced practical AIBs.

Boosting sodium-ion storage performance of MoSe2@C electrospinning nanofibers by embedding graphene nanosheets

In this work, a facile strategy for embedding graphene (GR) nanosheets into carbon-coated MoSe2 (MoSe2@C@GR) hybrid nanofibers has been developed by a simple electrospinning route. One dimensional nanofibers have excellent structural stability resulting from strong tolerance to stress change. The highly conductive graphene nanosheets play an excellent coating effect on MoSe2 to inhibit the growth of MoSe2 nanosheets on the nanofiber surface and enhance the conductivity of hybrid nanofibers, which substantially improves the rate performance and cycle stability of carbon-coated MoSe2 (MoSe2@C) nanofibers. In particular, the MoSe2@C@GR electrode delivers a high discharge capacity of 366.9 mAh g−1 after 200 cycles at 0.2 A g−1, meanwhile exhibits superior rate performance. The analysis of Nyquist plots reveals that the addition of graphene nanosheets can greatly strengthen the kinetics of electrode reaction and the electrochemical activity.

Enhanced the electrochemical performance of Li4Ti5O12 anode materials by high conductive graphene nanosheets

Li4Ti5O12/graphene nanosheets (LTO/GNSs) composites are prepared in situ via a sol–hydrothermal process. The LTO are found on the edges and surface of the GNSs, and GNSs give a conductive connection of LTO spheres to constitute a conductive network to improve the specific capacity and high-rate performance of LTO. With the increase of the amount of graphene nanosheets from 0 to 10 wt%, the electrical conductivity of composites increase from 1.78 × 10−9 S cm−1 to 2.04 S cm−1. However, the specific capacity of LTO/GNSs-10 wt% electrode at lower rate (≤5 C) (1C = 175 mAh g−1) is not greater than that of LTO electrode because of the high content of GNSs and the low specific capacity of GNSs at the potential range of 1.0 and 2.5 V. But at higher-rate (10 and 20 C in the investigation), electrical conductivity becomes the main factor affecting the specific capacity, so its specific capacity is greater than that of LTO electrode. LTO/GNSs-3 wt% composite shows the highest specific capacity and the best high-rate performance with good cycling performance. The significantly improved high-rate capability of the LTO/GNSs composites are mainly attributed to the improved electrical conductivity, the lower polarization of potential difference, the larger diffusion coefficient of lithium ion and smaller charge transfer resistance than LTO electrode.

Fabrication of Graphene/TiO2/Paraffin Composite Phase Change Materials for Enhancement of Solar Energy Efficiency in Photocatalysis and Latent Heat Storage

To enhance the solar energy utilization efficiency of microencapsulated phase change materials (PCMs), a novel composite system was designed by combination of graphene nanosheets and the microencapsulated n-eicosane with a brookite TiO2 shell. A series of n-eicosane@TiO2@graphene microcapsules were fabricated through interfacial polycondensation in an emulsion templating system, and their microstructures, chemical compositions and crystallinity were investigated extensively. The composite system presented a spherical core–shell structural morphology, where graphene nanosheets were attached onto the microcapsule surfaces through hydrogen bonding. The composite system achieved phase-change enthalpies over 160 J/g, and its thermal conductivity was also improved from 0.64 to 0.98 W·m–1·K–1 due to highly thermally conductive graphene nanosheets. This study confirmed that the introduction of graphene nanosheets was an effective way not only to improve the structural stability and serving durability of the compo...

Heat transport enhancement of heat sinks using Cu-coated graphene composites

Thermally conductive graphene nanosheets (GNs) decorated with Cu nanoparticles or nanoclusters are synthesized through an efficient microwave-assisted (MA) route followed by thermal reduction. The MA approach incorporated with thermal reduction is capable of uniformly disperse Cu deposits onto GNs, forming Cu/GN heterogeneous films. The dependence of thermal conductivity (k) on the amount of Cu deposits displays a general increasing trend as the Cu loading increases from 15.4 to 51.2 wt%. The k value of Cu/GN films can attain as high as 1912 W/m K at 50 °C. With the aid of Cu deposits, a remarkably improved electrical conductivity (σ) of Cu/GN heterogeneous films is observed, and the relation of k versus σ is also investigated. The enhanced k and σ values is attributed to the fact that the Cu deposits serve not only as interconnecting points but also as fillers, forming stereo conductive framework for thermal transport and electronic conduction. To inspect thermal properties, we employ one software (Comsol, pseudo 3D model) to simulate thermal conduction on Cu, GN, and Cu/GN heat sinks. The simulation result reveals that the Cu/GN heat sink displays more efficient thermal transport as compared to the others. As a result, this work proves that the robust design of Cu/GN heterogeneous film offers an integrated skeleton for thermal diffusivity, benefiting practical applications such as Si-based integrated chip.

Hydrothermally Synthesized Reduced Graphene Oxide-NiWO4 Nanocomposite for Lithium-Ion Battery Anode

Binary transition metal oxides have attracted wide attention in Li-ion batteries due to their multivalent electronic states and improved electrical conductivity. In this context, we have, for the first time, successfully synthesized reduced graphene oxide- nickel tungstate (RGO/NiWO4) nanocomposites by one pot hydrothermal method and employed them as anode for Li-ion battery. Scanning and transmission electron microscopic images show complete dispersion of NiWO4 nanoparticles (NPs) of size 20–50 nm on reduced graphene oxide sheets. The synthesized nanocomposites RGO/NiWO4 (1–3) (RGO:NiWO4 wt ratios of 50:50, 25:75 and 15:85) exhibit enhance electrochemical performance and cycling stability as compared to bare NiWO4 NPs. The electrodes made with bare NiWO4, RGO/NiWO4-1, RGO/NiWO4-2 and RGO/NiWO4-3 nanocomposites deliver specific capacities of 67, 578, 647 and 498 mAh g−1 respectively at 100 mA g−1 current density after 100 cycles achieving 98% coulombic efficiency. The improved cycling performance of nanocomposite is attributed to the incorporation of conducting graphene nanosheets, which not only act as flexible confinements but also prevent the detachment, agglomeration and pulverization of NiWO4 NPs. The excellent electrochemical performance of nanocomposite electrode in terms of specific capacity, cycling stability and rate capability makes it an ideal anode material for lithium ion battery.

Pomegranate-Like Silicon/Nitrogen-doped Graphene Microspheres as Superior-Capacity Anode for Lithium-Ion Batteries

Herein, pomegranate-like Silicon/Nitrogen-doped graphene microspheres (PSNGM) constructed by individual Si nanoparticle core wrapped by flexible nitrogen-doped reduced graphene oxide nanosheets (NG) have been synthesized through a facile and industrially large-scale spray drying approach. The PSNGM anode delivers excellent electrochemical performance: the reversible specific capacity at 100mAg−1 remains as large as 1141.6mAhg−1 after 150 cycles, with a high capacity retention of 96.1% from 2nd to 150th cycle; the capacity at 100mAg−1 can recover back to ∼1340mAhg−1 even after suffering a high current density of 5000mAg−1. The excellent performance is attributed to the unique pomegranate-like structure, nanoparticlization of Si and nitrogen doping of graphene: the pomegranate-like skeleton forms a highly conductive network, in which each Si nanoparticle is homogenously wrapped by flexible and conductive N-doped graphene nanosheets; flexible porous pomegranate-like structure can effectively accommodate the large volume variation during cycling; the N-doped graphene matrix guarantees its high conductivity for better electron and ion kinetics. The presented spray drying strategy is facile, low-cost and effective for large-scale industrial production of Si/graphene composite anode, and it can also be extended to fabricating other high-capacity electrode materials with low conductivities and large volume expansion.

Hydrothermal synthesis of graphene nanosheets and its application in electrically conductive adhesives

A highly electrical conductive adhesive based on graphene nanosheets (GNs) was developed. In this study, we prepared highly electrical conductive GNs via a green and efficient method and investigated the influence of graphene materials on the properties of electrically conductive adhesives. Primarily aimed at improving the electrical conductivity properties of electrically conductive adhesives (ECAs), graphene nanosheets was dispersed into an epoxy matrix to play a role as a network for providing a carrier transfer pathway. The results demonstrate that filling graphene nanosheets and microsilver flakes obviously decrease the resistivity of electrically conductive adhesives. Further, with increasing the graphene nanosheets content, resistivity sharply decreases. With a filling ratio up to 0.5% and the filling of 69.5% with microsilver flakes, the lowest resistivity has been reached 5.0×10−5Ωcm.

Cell-Instructive Graphene-Containing Nanocomposites Induce Multinucleated Myotube Formation.

Myoblast differentiation is a key step in myogenesis and has long been considered to be controlled mainly by biochemical cues such as growth factors. However, the tissue engineering approaches based on biochemical cues demonstrate low reproducibility as a precise spatial control over their bioactivity is challenging. Recently, substrate micro/nano-structure and electro-responsive properties are recognized for their important roles in myoblast differentiation. In this study, we hypothesized that engineering biophysical features such as nano/micro-fibrous structure and conductive properties into a single biomaterial scaffold will instruct the myoblasts to differentiate into multinucleated myotubes even in the absence of differentiation media. We fabricated nanocomposite scaffolds composed of conductive graphene nanosheets and polycaprolactone (PCL), a widely used biocompatible material. The resulting graphene-PCL scaffolds possess excellent conductivity due to graphene nanosheets and great processability, biodegradability and elastic mechanical properties conferred by PCL. Additionally, physicochemical and mechanical properties of nanocomposite scaffolds can be tuned by varying graphene concentration. Further, graphene-PCL nanocomposites and their 8-week degradation products exhibited remarkable cytocompatibility and promoted adhesion and proliferation of C2C12 mouse myoblast cells. Importantly, these nanocomposite scaffolds induced graphene concentration-dependent differentiation of C2C12 cells into multinucleated myotubes even in normal growth media suggesting their cell-instructive potential. Thus, graphene-PCL nanocomposite scaffolds can serve as a strategy to promote skeletal muscle regeneration without biochemical cues.

Electrospun Lotus Root-like CoMoO4@Graphene Nanofibers as High-Performance Anode for Lithium Ion Batteries

Lotus root-like CoMoO4@graphene nanofibers(CoMoO4@G NFs) was prepared by electrospinning along with post heat treatment, and used as high-performance anode for lithium ion batteries (LIBs). Compared with the pure CoMoO4 NFs, the prepared lotus root-like CoMoO4@G NFs electrode displays higher reversible capacity of 735mAhg−1 at 100mAg−1, better rate capability and cycling stability (capacity retains 80% based on the second cycle even after 200 cycles,). These results highlight the importance of combination of conductive graphene nanosheets with multi-level porous CoMoO4 NFs for high-performance LIBs.

Electrochemistry of Multilayers of Graphene and Myoglobin Modified Electrode and Its Biosensing

AbstractA multilayers of graphene (GR) and myoglobin (Mb) modified electrode was fabricated with a layer of chitosan film. Electrochemical behaviors of the modified electrode were studied by cyclic voltammetry, which exhibited a couple of well‐behaved, stable and quasi‐reversible cathodic and anodic peaks, indicating that Mb realized its direct electron transfer on the biosensor. The experimental result may be accredited to the existence of multilayers conductive GR nanosheets that could provide big specific surface area, fine biological compatibility and ultrahigh electron transfer route for the immobilized Mb. The catalytic reduction peak currents of the biosensor to the detection of trichloroacetic acid were established from 0.6 to 26.0 mM accompanied with the detection limit as 0.15 mM (3σ). Therefore a novel third‐generation mediator‐free electrochemical sensor was successful prepared with the usage of multilayers of GR.

Using silver nanocluster/graphene nanocomposite to enhance photoelectrochemical activity of CdS:Mn/TiO2 for highly sensitive signal-on immunoassay

A highly sensitive signal-on photoelectrochemical (PEC) immunosensor was fabricated here using CdS:Mn/TiO2 as photoelectrochemical sensing platform, and silver nanoclusters and graphene naocomposites (AgNCs-GR) as signal amplification tags. The immunosensor was constructed based on the specific sandwich immunoreaction, and the photo-to-current conversion efficiency of the isolated protein modified CdS:Mn/TiO2 matrix was improved based on the synergistic effect of AgNCs-GR. Under irradiation, the photogenerated electrons from the AgNCs at a higher conduction band edge level could be transport to the CdS:Mn/TiO2 matrix with the assistance of highly conductive graphene nanosheets, as well as recycle the trapped excitons in the defects-rich CdS:Mn/TiO2 interface. The electron transport and exciton recycle reduced the possibility of electron–hole recombination and greatly improved the photo-to-current conversion efficiency of the sensing matrix. Based on the signal enhancement, a signal-on PEC immunosensors was fabricated for the detection of carcinoembryonic antigen (CEA), a model analyte related to many malignant diseases. Under optimal conditions, the as-prepared immunosensor showed excellent analytical performance, with a wide linear range from 1.0pg/mL to 100ng/mL and a low limit of detection of 1.0pg/mL. The signal-on mode provided 2.48 times higher sensitivity compared with signal-off mode. This strategy demonstrated good accuracy and high selectivity for practical sample analysis, thus may have great application prospective in the prediction and early diagnosis of diseases.

A novel acetylene black/sulfur@graphene composite cathode with unique three-dimensional sandwich structure for lithium-sulfur batteries

A novel acetylene black/sulfur@graphene composite (AB/S@G) with unique three-dimensional sandwich structure was successfully prepared via an in situ sulfur deposition strategy and self-assembly. Acetylene black as conductive carbon skeleton and graphene nanosheets as physical shields played an extremely important role for improving the electrochemical performances of the AB/S@G cathode. Compared with the AB/S cathode, the AB/S@G cathode with a sulfur content of 54wt% exhibited a high utilization of sulfur, an enhanced cyclical stability, and an excellent rate capability. The AB/S@G cathode came true a high sulfur utilization of 95.73% after undergoing a high initial discharge capacity of 1603.5mAhg−1 at a current density of 200mAg−1, much higher than that (71.78%) of the AB/S cathode. The excellent electrochemical performances were principally attributed to the combined effect of graphene nanosheets and acetylene black, which provided an improved electrical conductivity for the sulfur cathode, effective restraining for soluble polysulfides, and powerful buffer for the volume changes of sulfur during cycling.

Self-assembled CoS2 nanoparticles wrapped by CoS2-quantum-dots-anchored graphene nanosheets as superior-capability anode for lithium-ion batteries

For the first time, self-assembled CoS2 nanoparticles wrapped by CoS2-quantum-dots anchored graphene nanosheets (CoS2NP@G-CoS2QD) are synthesized by a facile l-cysteine-assisted hydrothermal reaction. When the composite is used as anode in lithium-ion batteries (LIBs), it shows superior electrochemical performance: the reversible specific capacity is as large as 1048mAhg−1; the 300th-cycle capacity still maintains 831mAhg−1 even at 1Ag−1; the rate capacity remains 411mAhg−1 even at 10Ag−1, which is the highest value ever reported at such high current density for CoS2 based materials. The excellent electrochemical performance is attributed to the unique structure with CoS2 nanoparticles homogeneously wrapped by highly flexible and conductive few-layer graphene nanosheets adhering abundant CoS2 quantum dots, which can effectively suppress the aggregation of CoS2 nanoparticles, accommodate the volume change during the cycle processes and maintain high electrical conductivity of the electrode. The CoS2NP@G-CoS2QD composite is promising for superior-capability anode for LIBs and can be further extended to broad applications in supercapacitors, sensors, and catalysis.

Preparation of Solution-Processable Reduced Graphene Oxide/Polybenzoxazole Nanocomposites with Improved Dielectric Properties

The abilities to enhance the degree of orientational freedom of dipole in polymer dielectrics and strengthen the homogeneous dispersion of conductive fillers in matrix are of crucial importance for fabricating composite materials with high dielectric constant, low dielectric loss, low density, and good processability. Compared with conventional main-chain polybenzoxazoles, whose processability and dielectric performance are strictly limited by the conjugated benzoxazole groups on the backbone, improved solubility in dimethylformamide and dielectric constant (4.92) were observed for poly(2-isopropenylbenzoxazole) (P(2-IBO)), due to the high mobility of the dipole (benzoxazole ring) on the side chains. In addition, improved dispersion of conductive graphene nanosheets was achieved by a surface-initiated atom transfer radical polymerization (ATRP) of the N-(2-hydroxyphenyl)methacrylamide (o-HPMAA), the precursor of 2-isopropenylbenzoxazole from reduced graphene oxide (RGO). The nanocomposites of functionalized graphene and P(2-IBO) possess a dielectric constant of 8.35 (approximately 70% higher than that of pure P(2-IBO) at 1 kHz) when the weight fraction of functionalized graphene reaches 0.015, the lowest so far among the reports on dielectric property of the graphene/polybenzoxazole system.

Synthesis and characterization of conductive few layered graphene nanosheets using an anionic electrochemical intercalation and exfoliation technique

Few layered conductive graphene nanosheets have been synthesized using a protic intercalate electrolyte in a two electrode electrochemical intercalation and exfoliation process.

Synergistic effect of manganese oxide nanoparticles and graphene nanosheets in composite anodes for lithium ion batteries

A graphene-Mn3O4-graphene (GMG) sandwich structure with homogeneous anchoring of Mn3O4 nanoparticles among flexible and conductive graphene nanosheets (GSs) is achieved through dispersion of the GSs in Mn(NO3)2 solution and subsequent calcination. Mn3O4 nanoparticles are 50 ∼ 200 nm clusters consisting of 10 ∼ 20 nm primary particles, and serve as spacers to prevent the re-stacking of the GSs. GSs provide a highly conductive network among Mn3O4 nanoparticles for efficient electron transfer and buffer any volume change during cycling. Due to the strong synergistic effect between Mn3O4 and GSs, the capacity contributions from GSs and Mn3O4 in GMG are much larger than capacities of pure GSs and Mn3O4. Consequently, the GMG composite electrodes show excellent electrochemical properties for lithium ion battery applications, demonstrating a large reversible capacity of 750 mAh g−1 at 0.1 C based on the mass of GMG with no capacity fading after 100 cycles, and high rate abilities of 500 mAh g−1 at 5 C and 380 mAh g−1 at 10 C.

Ultrasmall Li2S nanoparticles anchored in graphene nanosheets for high-energy lithium-ion batteries.

Li2S has a high theoretical capacity of 1166 mAh g−1, but it suffers from limited rate and cycling performance. Herein we reported in-situ synthesis of thermally exfoliated graphene−Li2S (in-situ TG−Li2S) nanocomposite and its application as a superior cathode material alternative to sulfur. Li2S nanoparticles with the size of ~8.5 nm homogeneously anchored in graphene nanosheets were prepared via chemical reduction of pre-sublimed sulfur by lithium triethylborohydride (LiEt3BH). The in-situ TG−Li2S nanocomposite exhibited an initial capacity of 1119 mAh g−1 Li2S (1609 mAh g−1 S) with a negligible charged potential barrier in the first cycle. The discharge capacity retained 791 mAh g−1 Li2S (1137 mAh g−1 S) after 100 cycles at 0.1C and exceeded 560 mAh g−1 Li2S (805 mAh g−1 S) at a high rate of 2C. Moreover, coupling the composite with Si thin film anode, a Li2S/Si full cell was produced, delivering a high specific capacity of ~900 mAh g−1 Li2S (1294 mAh g−1 S). The outstanding electrode performance of in-situ TG−Li2S composite was attributed to the well dispersed small Li2S nanoparticles and highly conductive graphene nanosheets, which provided merits of facile ionic and electronic transport, efficient utilization of the active material, and flexible accommodation of volume change.

Synthesis of nano-sized ZnCo2O4 anchored with graphene nanosheets as an anode material for secondary lithium ion batteries

ZnCo2O4/graphene and pure ZnCo2O4 nanoparticles were synthesized by simple and low temperature urea-assisted auto-combustion method and annealed at 400°C for 5h in air atmosphere. The electron microscopy image of the obtained ZnCo2O4/graphene nanocomposite revealed that the ZnCo2O4 nanoparticles were randomly distributed and anchored on the surface of reduced graphene nanosheets. The graphene nanosheets significantly reduced the particles size and suppressed the aggregation of ZnCo2O4 nanoparticles as well as maintaining the good electrical conductivity of the overall sample. The size of the nanoparticles was in the range of 50–100nm and the size of nanoparticles in the nanocomposite sample in the range of 25–50nm. The electrochemical results showed that the ZnCo2O4/graphene nanocomposite electrode had greatly improved cycling stability with high reversible capacity of 755.6 mAh g−1 after 70 cycles, and better rate capability of 378.1 mAh g−1 at 4.5C than pure ZnCo2O4 nanoparticles (299.8 mAh g−1 after 70 cycles and 302.4 mAh g−1 at 4.5C). The enhanced electrochemical performance of the nanocomposite could be ascribed to the positive synergistic effect of the combination of the ZnCo2O4 nanoparticles and conducting graphene nanosheets.