Graphene-based Hybrid Materials Research Articles

Highly Conductive Nitrogen-Doped Graphene Grown on Glass toward Electrochromic Applications.

The direct synthesis of low sheet resistance graphene on glass can promote the applications of such intriguing hybrid materials in transparent electronics and energy-related fields. Chemical doping is efficient for tailoring the carrier concentration and the electronic properties of graphene that previously derived from metal substrates. Herein, we report the direct synthesis of 5 in. uniform nitrogen-doped (N-doped) graphene on the quartz glass through a designed low-pressure chemical vapor deposition (LPCVD) route. Ethanol and methylamine were selected respectively as precursor and dopant for acquiring predominantly graphitic-N-doped graphene. We reveal that by a precise control of growth temperature and thus the doping level the sheet resistance of graphene on glass can be as low as one-half that of nondoped graphene, accompanied by relative high crystal quality and transparency. Significantly, we demonstrate that this scalable, 5 in. uniform N-doped graphene glass can serve as excellent electrode materials for fabricating high performance electrochromic smart windows, featured with a much simplified device structure. This work should pave ways for the direct synthesis and application of the new type graphene-based hybrid material.

Reaction of Co3O4 Nanocrystals on Graphene Sheets to Fabricate Excellent Catalysts for Hydrogen Generation

The development of functionalized graphene is of significant importance for the application of graphene in solving current energy and environmental problems. In this work, a series of graphene-based hybrid materials including porous graphene (PG) and carbon nanofibers anchored graphene oxide (GCNFs) were synthesized adopting a controllable solid-phase reaction strategy. Co3O4 nanocrystals (NCs) were used as oxidants to modify and adjust graphene sheets. The PG and GCNFs were formed crucially through the red-ox reaction between graphene and Co3O4 NCs during calcinations. As catalyst for NaBH4 hydrolysis at room temperature, CoOx NCs anchored onto PG and CoOx NCs anchored onto GCNFs provided hydrogen generation specific rates of 1472 mL·min–1·gCo–1 and 2696 mL·min–1·gCo–1, respectively. These outstanding catalytic activities are attributed to the synergistic effect of CoOx NCs and PG/GCNFs. A general strategy was proposed for the oxidative cutting and reconstruction of graphene sheets, and the preparation o...

Hybrid Graphene-Polyoxometalates Nanofluids as Liquid Electrodes for Dual Energy Storage in Novel Flow Cells.

Solid Hybrid materials abound. But flowing versions of them are new actors in the materials science landscape and in particular for energy applications. This paper presents a new way to deliver nanostructured hybrid materials for energy storage, namely, in the form of nanofluids. We present here the first example of a hybrid electroactive nanofluid (HENFs) combining capacitive and faradaic energy storage mechanisms in a single fluid material. This liquid electrode is composed of reduced graphene oxide and polyoxometalates (rGO-POMs) forming a stable nanocomposite for electrochemical energy storage in novel Nanofluid Flow Cells. Two graphene based hybrid materials (rGO-phosphomolybdate, rGO-PMo12 and rGO-phosphotungstate, rGO-PW12 ) were synthesized and dispersed with the aid of a surfactant in 1 M H2 SO4 aqueous electrolyte to yield highly stable hybrid electroactive nanofluids (HENFs) of low viscosity which were tested in a home-made flow cell under static and continuous flowing conditions. Remarkably, even low concentration rGO-POMs HENFs (0.025 wt%) exhibited high specific capacitances of 273 F/g(rGO-PW12 ) and 305 F/g(rGO-PMo12 ) with high specific energy and specific power. Moreover, rGO-POM HENFs show excellent cycling stability (∼95 %) as well as Coulombic efficiency (∼77-79 %) after 2000 cycles. Thus, rGO-POM HENFs effectively behave as real liquid electrodes with excellent properties, demonstrating the possible future application of HENFs for dual energy storage in a new generation of Nanofluid Flow Cells.

Design of CdTeSe–Porphyrin–Graphene Composite for Photoinduced Electron Transfer and Photocurrent Generation

Considerable attention has been paid to designing graphene based hybrid materials for developing new light-harvesting systems. Here, we have synthesized CdTeSe alloy nanorods and modified the surface of CdTeSe nanorods by porphyrin molecules to attach to graphene surface through π–π stacking. In this CdTeSe nanorod–porphyrin–graphene hybrid system, porphyrin acts as an antenna material which harvests light and consequently transfers electrons to the adjacent conduction band of nanorods and finally to reduced graphene oxide (RGO). An ultrafast spectroscopic study suggests that the rate of electron transfer from porphyrin to RGO via conduction band of CdTeSe nanorods is 17.4 × 10–2 ps–1. It is to be noted that this ternary hybrid system exhibits 240-fold enhancement of photocurrent under visible light irradiation which reveals that this new type of graphene based inorganic and organic hybrid system is very promising for solar light harvesting.

Acid-free co-operative self-assembly of graphene-ZnO nanocomposites and its defect mediated visible light photocatalytic activities

We propose an acid-free and environmental friendly surfactant based approach to anchor zinc oxide (ZnO) nanoparticles on graphene. Herein, liquid-phase exfoliated graphene in water by ultrasonic waves has been used to prepare graphene-ZnO (G-ZnO) nanocomposites that circumvent the use of various toxic acids and chemicals which are generally used in the preparation of graphene-based nanocomposites. Oxygen vacancy related defect peaks observed by Raman and photoluminescence confirm the formation of C–O–Zn bond due to the synergistic interaction of carbon and zinc via oxygen atoms in G-ZnO nanocomposites. The enhanced photocatalytic behavior of G-ZnO under visible light as evaluated using the dye Rhodamine B holds its genesis from the intrinsic oxygen defects in G-ZnO. Furthermore, graphene acts as electron sink for accumulation of charges from defect levels of ZnO, which controls recombination of charge carriers. It is envisaged that the acid-free and facile strategy can be a potential route for the preparation of graphene-based hybrid materials using liquid-phase exfoliation methodology.

Fabrication of self-healing and hydrophilic coatings from liquid-like graphene@SiO2 hybrids

Functionalized liquid-like graphene@SiO2 hybrids are fabricated by using the graphene@SiO2 as core and nonionic copolymer as shell in aqueous solution at room temperature. The hybrid materials can flow above 45 °C and have a particular thermal invertibility. The morphology, chemical composition, dispersibility and stability, as well as rheological behavior are systematically characterized by various methods. It is shown that well-dispersed SiO2 nanoparticles are tightly anchored on the surface of graphene sheet via hydrogen bonding interaction under the synergetic effect of 3-(trimethoxysilyl)-1-propanethiol and copolymer to prevent the aggregation of graphene sheet. What is more, the hybrid materials keep remarkably stability and dispersibility in organic solvents and aqueous solution. More importantly, rheological tests indicate that viscoelastic behavior of graphene@SiO2 hybrids is effectively regulated through varying the amount of surface nonionic copolymer and silane coupling agent, respectively. In addition, the liquid-like graphene@SiO2 hybrids as a novel of hybrid coating make the substrates transfer from hydrophobicity to hydrophilicity. More interestingly, the damaged coating can be self-healed under immersing water or heating conditions, respectively. This simple and environment friendly approach will benefit for fabricating large scale graphene based hybrid materials in application of functional coating and rheological additives.

Catalytic reduction of CO2 to alcohol with Cu2Se-combined graphene binary nanocomposites

ABSTRACTPhotocatalytic reduction of CO2 over a Cu2Se–graphene nanocatalyst has been investigated. The nanocomposite material was successfully prepared via a modified hydrothermal method. The structure and properties of the prepared composite were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray microscopy, transmission electron microscopy, Raman spectroscopic analysis, and X-ray photoelectron spectroscopy. A synergetic effect of the combination of Cu2Se and graphene appeared in the form of excellent photocatalytic reduction capability of CO2. The photocatalytic efficiencies of the samples were characterized by testing for the photoreduction of CO2 to alcohol under visible light irradiation, which produced results such as to suggest that there is a significant potential for graphene-based semiconductor hybrid materials to be used as photocatalysts for reduction of CO2.

Combined Molecular Dynamics and Density Functional Theory Study of Azobenzene–Graphene Interfaces

The electronic properties of graphene can be tuned in a dynamic way from physical adsorption of molecular photoswitches. Here, we first investigate the formation of 4-(decyloxy)azobenzene molecular monolayers on a single graphene layer through molecular dynamics (MD) simulations and assess the associated change in work function (WF) at the density functional theory (DFT) level. We show that the major contribution to the WF shift arises from electrostatic effects induced by the azobenzene electric dipole component normal to graphene and that the conformational distribution of the molecular switches in either their trans or cis forms can be convoluted into WF distributions for the hybrid systems. We next use this strategy to build a statistical ensemble for the work functions of graphene decorated with fluorinated azobenzene derivative designed to maximize the change in WF upon photoswitching. These findings pave the way to the possible use of photoswitchable graphene-based hybrid materials as optically con...

Applications of Graphene-Based Hybrid Material as Electrodes in Microbial Fuel Cells

Applications of Graphene-Based Hybrid Material as Electrodes in Microbial Fuel Cells

3D graphene-based hybrid materials: synthesis and applications in energy storage and conversion.

Porous 3D graphene-based hybrid materials (3D GBHMs) are currently attractive nanomaterials employed in the field of energy. Heteroatom-doped 3D graphene and metal, metal oxide, and polymer-decorated 3D graphene with modified electronic and atomic structures provide promising performance as electrode materials in energy storage and conversion. Numerous synthesis methods such as self-assembly, templating, electrochemical deposition, and supercritical CO2, pave the way to mass production of 3D GBHMs in the commercialization of energy devices. This review summarizes recent advances in the fabrication of 3D GBHMs with well-defined architectures such as finely controlled pore sizes, heteroatom doping types and levels. Moreover, current progress toward applications in fuel cells, supercapacitors and batteries employing 3D GBHMs is also highlighted, along with the detailed mechanisms of the enhanced electrochemical performance. Furthermore, current critical issues, challenges and future prospects with respect to applications of 3D GBHMs in practical devices are discussed at the end of this review.

Single-Step Functionalization and Exfoliation of Graphene with Polymers under Mild Conditions.

The simultaneous polymer functionalization and exfoliation of graphene sheets by using mild bath sonication and heat treatment at low temperature is described. In particular, free-radical polymerization of three different vinyl monomers takes place in the presence of graphite flakes. The polymerization procedure leads to the exfoliation of graphene sheets and at the same time the growing polymer chains are attached onto the graphene lattice, which gives solubility and stability to the final graphene-based hybrid material. The polymer-functionalized graphene sheets possess fewer defects as compared with previously reported polymer-functionalized graphene. The success of the covalent functionalization and exfoliation of graphene was confirmed by using a variety of complementary spectroscopic, thermal, and microscopy techniques, including Raman, IR and UV/Vis spectroscopy, thermogravimetric analysis, and transmission electron microscopy.

Reductive hybridization route with exfoliated graphene oxide and MoS2 nanosheets to efficient electrode materials

Mesoporous MoS2–graphene nanohybrid with excellent electrode activity can be synthesized by the reductive hybridization of exfoliated MoS2 and graphene oxide (G-O) nanosheets under hydrothermal condition. The use of G-O precursor is crucial in synthesizing homogeneously hybridized MoS2–graphene materials with mesoporous stacking structure. The MoS2–graphene nanohybrid prepared with G-O shows promising electrode performance for lithium ion batteries with large discharge capacity of ∼1400mAhg−1 for the 100th cycle and excellent rate performance, which is much superior to that of the homologue prepared with rG-O precursor and also restacked MoS2 nanosheets. The present results clearly demonstrate the usefulness of G-O precursor in the hydrothermal synthesis of graphene-based hybrid materials.

Role of grain boundaries in tailoring electronic properties of polycrystalline graphene by chemical functionalization

Grain boundaries, inevitably present in chemical vapor deposited graphene, are expected to have considerable impact on the development of graphene-based hybrid materials with tailored material properties. We demonstrate here the critical role of polycrystallinity on the chemical functionalization of graphene comparing ozone-induced oxidation with remote plasma hydrogenation. We show that graphene oxidation and hydrogenation occur in two consecutive stages upon increasing defect density: an initial step in which surface-bound functional groups are generated, followed by the creation of vacancies. Remarkably, we find that hydrogenation yields homogeneously distributed defects while ozone-induced defects are preferentially accumulated at the grain boundaries eventually provoking local cracking of the structure. Supported by quantum simulations, our experimental findings reveal distinct electronic transport regimes depending on the density and distribution of induced defects on the polycrystalline graphene films. Our findings highlight the key role played by grain boundaries during graphene functionalization, and at the same time provide a novel perspective to tailor the properties of polycrystalline graphene.

A Bottom-Up Approach for the Synthesis of Highly Ordered Fullerene-Intercalated Graphene Hybrids

Much of the research effort on graphene focuses on its use as a building block for the development of new hybrid nanostructures with well-defined dimensions and properties suitable for applications such as gas storage, heterogeneous catalysis, gas/liquid separations, nanosensing and biomedicine. Towards this aim, here we describe a new bottom-up approach, which combines self-assembly with the Langmuir Schaefer deposition technique to synthesize graphene-based layered hybrid materials hosting fullerene molecules within the interlayer space. Our film preparation consists in a bottom-up layer-by-layer process that proceeds via the formation of a hybrid organo-graphene oxide Langmuir film. The structure and composition of these hybrid fullerene-containing thin multilayers deposited on hydrophobic substrates were characterized by a combination of X-ray diffraction, Raman and X-ray photoelectron spectroscopies, atomic force microscopy and conductivity measurements. The latter revealed that the presence of C60 within the interlayer spacing leads to an increase in electrical conductivity of the hybrid material as compared to the organo-graphene matrix alone.

Cu–BTC MOF–graphene-based hybrid materials as low concentration ammonia sensors

The synergistic effect on conductivity of Cu–BTC MOF–graphene-based hybrid material components allows their application as ammonia sensing materials.

Donor–acceptor graphene-based hybrid materials facilitating photo-induced electron-transfer reactions

Graphene research and in particular the topic of chemical functionalization of graphene has exploded in the last decade. The main aim is to increase the solubility and thereby enhance the processability of the material, which is otherwise insoluble and inapplicable for technological applications when stacked in the form of graphite. To this end, initially, graphite was oxidized under harsh conditions to yield exfoliated graphene oxide sheets that are soluble in aqueous media and amenable to chemical modifications due to the presence of carboxylic acid groups at the edges of the lattice. However, it was obvious that the high-defect framework of graphene oxide cannot be readily utilized in applications that are governed by charge-transfer processes, for example, in solar cells. Alternatively, exfoliated graphene has been applied toward the realization of some donor–acceptor hybrid materials with photo- and/or electro-active components. The main body of research regarding obtaining donor–acceptor hybrid materials based on graphene to facilitate charge-transfer phenomena, which is reviewed here, concerns the incorporation of porphyrins and phthalocyanines onto graphene sheets. Through illustrative schemes, the preparation and most importantly the photophysical properties of such graphene-based ensembles will be described. Important parameters, such as the generation of the charge-separated state upon photoexcitation of the organic electron donor, the lifetimes of the charge-separation and charge-recombination as well as the incident-photon-to-current efficiency value for some donor–acceptor graphene-based hybrids, will be discussed.

Intercalation study of low-molecular-weight hyperbranched polyethyleneimine into graphite oxide.

We report for the first time the intercalation of low-molecular-weight hyperbranched polyethyleneimine (PEI) into graphite oxide (GO) for the facile, bulk synthesis of novel graphene-based hybrid (GO-PEI) materials exhibiting tailored interlayer galleries. The size of the intercalant as well as the loading in GO were systematically investigated to determine their contribution to the basal spacing of the resulting materials. Powder X-ray diffraction measurements demonstrated the generation of constrained hybrid systems along the c axis that exhibit considerably increased interlayer distances compared with the starting, pristine GO. The results of X-ray photoelectron and FTIR studies are consistent with a "grafting-to" process of the intercalated PEI with the oxygen functional groups present along the GO framework. Furthermore, it was found that a great number of the nitrogen-containing groups in PEI still remain available within the newly formed, confined micro-environment of intercalated GO galleries. The increased surface area of the GO-PEI hybrids in conjunction with the remaining available active groups of intercalated PEI render the synthesised hybrids very attractive candidates as nanostructured adsorbents.

Tensile properties of a boron/nitrogen-doped carbon nanotube-graphene hybrid structure.

Doping is an effective approach that allows for the intrinsic modification of the electrical and chemical properties of nanomaterials. Recently, a graphene and carbon nanotube hybrid structure (GNHS) has been reported, which extends the excellent properties of carbon-based materials to three dimensions. In this paper, we carried out a first-time investigation on the tensile properties of the hybrid structures with different dopants. It is found that with the presence of dopants, the hybrid structures usually exhibit lower yield strength, Young’s modulus, and earlier yielding compared to that of a pristine hybrid structure. For dopant concentrations below 2.5% no significant reduction of Young’s modulus or yield strength could be observed. For all considered samples, the failure is found to initiate at the region where the nanotubes and graphene sheets are connected. After failure, monatomic chains are normally observed around the failure region. Dangling graphene layers without the separation of a residual CNT wall are found to adhere to each other after failure with a distance of about 3.4 Å. This study provides a fundamental understanding of the tensile properties of the doped graphene–nanotube hybrid structures, which will benefit the design and also the applications of graphene-based hybrid materials.

High performance graphene/manganese oxide hybrid electrode with flexible holey structure

Graphene with flexible holey structure (HRGO) is firstly prepared by a wet chemical method in mild acid oxidation, and then graphene/manganese oxide hybrid nanocomposite with holey structure (HRGO/α–MnO2) is prepared by hydrothermally treating an isopropyl alcohol suspension of HRGO, MnCl2·4H2O, and KMnO4 at 90°C for 1h. α–MnO2 with needle–like morphology is uniformly dispersed on the surface of HRGO nanosheets, which prevents the restacking of the graphene nanosheets and allows graphene nanosheets to exist in a complete exfoliation state in HRGO/α–MnO2 hybrid material. The self–assembly between HRGO nanosheets and α–MnO2 particles can increase the specific surface area of the prepared material (about 196 m2g−1). The HRGO nanosheets improve the utilization efficiency of α–MnO2 in the hybrid electrode, while the holey structure provides a high density of porosity to facilitate charges and ions transport. The prepared electrode material exhibits a high specific capacitance of 348 F g−1 at 5mV s−1 in 1molL−1 Na2SO4 electrolyte with a capacitance retention of 86% after 1000 cycles at a constant current density of 10 A g−1. This preparation method may open new opportunity for preparing other types of graphene–based hybrid materials for technological applications.

A Flexible and High‐Voltage Internal Tandem Supercapacitor Based on Graphene‐Based Porous Materials with Ultrahigh Energy Density

Pursuing higher working voltage and packaged energy density, an internal tandem supercapacitor has been successfully designed and fabricated based on graphene-based porous carbon hybrid material. Compared with the packaged energy density of 27.2 Wh kgcell (-1) and working voltage of 3.5 V using EMIMBF4 electrolyte for the conventional single-cell supercapacitor, the internal tandem device with the same material achieves a much higher working voltage of 7 V as well as a significantly improved energy density of 36.3 Wh kgcell (-1) (increased by 33%), which is also about 7 times of that of the state-of-art commercial supercapacitors. A flexible internal tandem device is also designed and fabricated and demonstrated similar excellent performance.