In this present review, the current status of the intrinsic mechanical properties of the graphene-family of materials along with the preparation and properties of bulk graphene-based nanocomposites ...is thoroughly examined. The usefulness of Raman spectroscopy for the characterization and study of the mechanical properties of graphene flakes and their composites is clearly exhibited. Furthermore, the preparation strategies of bulk graphene-based nanocomposites are discussed and the mechanical properties of nanocomposites reported in the literature are analysed. In particular, through the analyse of several hundred literature papers on graphene composites, we have found a unique correlation between the filler modulus, derived from the rule of mixtures, and the composite matrix. This correlation is found to hold true across a wide range of polymer matrices and thus suggests that the common assumption that the filler modulus is independent of the matric is incorrect, explaining the apparent under performance of graphene in some systems. The presence of graphene even at very low loadings can provide significant reinforcement to the final material, while the parameters that affect the nanocomposite strongly are thoroughly reviewed. Finally, the potential applications and future perspectives are discussed with regard to scale up capabilities and possible developments of graphene-based nanocomposite materials.
Polymer nanocomposites reinforced with carbon-based nanofillers are gaining increasing interest for a number of applications due to their excellent properties. The understanding of the reinforcing ...mechanisms is, therefore, very important for the maximization of performance. This present review summarizes the current literature status on the mechanical properties of composites reinforced with graphene-related materials (GRMs) and carbon nanotubes (CNTs) and identifies the parameters that clearly affect the mechanical properties of the final materials. It is also shown how Raman spectroscopy can be utilized for the understanding of the stress transfer efficiency from the matrix to the reinforcement and it can even be used to map stress and strain in graphene. Importantly, it is demonstrated clearly that continuum micromechanics that was initially developed for fibre-reinforced composites is still applicable at the nanoscale for both GRMs and CNTs. Finally, current problems and future perspectives are discussed.
Conductive inks for the future printed electronics should have the following merits: high conductivity, flexibility, low cost, and compatibility with wide range of substrates. However, the ...state-of-the-art conductive inks based on metal nanoparticles are high in cost and poor in flexibility. Herein, we reported a highly conductive, low cost, and super flexible ink based on graphene nanoplatelets. The graphene ink has been screen-printed on plastic and paper substrates. Combined with postprinting treatments including thermal annealing and compression rolling, the printed graphene pattern shows a high conductivity of 8.81 × 104 S m–1 and good flexibility without significant conductivity loss after 1000 bending cycles. We further demonstrate that the printed highly conductive graphene patterns can act as current collectors for supercapacitors. The supercapacitor with the printed graphene pattern as the current collector and printed activated carbon as the active material shows a good rate capability of up to 200 mV s–1. This work potentially provides a promising route toward the large-scale fabrication of low cost yet flexible printed electronic devices.
We present a non-oxidative production route to few layer graphene via the electrochemical intercalation of tetraalkylammonium cations into pristine graphite. Two forms of graphite have been studied ...as the source material with each yielding a slightly different result. Highly orientated pyrolytic graphite (HOPG) offers greater advantages in terms of the exfoliate size but the source electrode set up introduces difficulties to the procedure and requires the use of sonication. Using a graphite rod electrode, few layer graphene flakes (2nm thickness) are formed directly although the flake diameters from this source are typically small (ca. 100–200nm). Significantly, for a solvent based route, the graphite rod does not require ultrasonication or any secondary physical processing of the resulting dispersion. Flakes have been characterized using Raman spectroscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS).
The preparation and characterisation of the different forms of graphene are reviewed first of all. The different techniques that have been employed to prepare graphene such as mechanical and solution ...exfoliation, and chemical vapour deposition are discussed briefly. Methods of production of graphene oxide by the chemical oxidation of graphite are then described. The structure and mechanical properties of both graphene and graphene oxide are reviewed and it is shown that although graphene possesses superior mechanical properties, they both have high levels of stiffness and strength. It is demonstrated how Raman spectroscopy can be used to characterise the different forms of graphene and also follow the deformation of exfoliated graphene, with different numbers of layers, in model composite systems. It is shown that continuum mechanics can be employed to analyse the behaviour of these model composites and used to predict the minimum flake dimensions and optimum number of layers for good reinforcement. The preparation of bulk nanocomposites based upon graphene and graphene oxide is described finally and the properties of these materials reviewed. It is shown that good reinforcement is only found at relatively low levels of graphene loading and that, due to difficulties with obtaining good dispersions, challenges still remain in obtaining good mechanical properties for high volume fractions of reinforcement.
Two-dimensional materials, such as graphene and molybdenum disulfide (MoS2), can greatly increase the performance of electrochemical energy storage devices because of the combination of high surface ...area and electrical conductivity. Here, we have investigated the performance of solution exfoliated MoS2 thin flexible membranes as supercapacitor electrodes in a symmetrical coin cell arrangement using an aqueous electrolyte (Na2SO4). By adding highly conductive graphene to form nanocomposite membranes, it was possible to increase the specific capacitance by reducing the resistivity of the electrode and altering the morphology of the membrane. With continued charge/discharge cycles the performance of the membranes was found to increase significantly (up to 800%), because of partial re-exfoliation of the layered material with continued ion intercalation, as well as increasing the specific capacitance through intercalation pseudocapacitance. These results demonstrate a simple and scalable application of layered 2D materials toward electrochemical energy storage.
Graphene shows considerable promise in structural composite applications thanks to its unique combination of high tensile strength, Young's modulus and structural flexibility which arise due to its ...maximal chemical bond strength and minimal atomic thickness. However, the ultimate performance of graphene composites will depend, in addition to the properties of the matrix and interface, on the morphology of the graphene used, including the size and shape of the sheets and the number of chemical defects present. For example, whilst oxidized sp3 carbon atoms and vacancies in a graphene sheet can degrade its mechanical strength, they can also increase its interaction with other materials such as the polymer matrix of a composite, thus maximizing stress transfer and leading to more efficient mechanical reinforcement. Herein, we present an overview of some recently published work on graphene mechanical properties and discuss a list of challenges that need to be overcome (notwithstanding the strong hype existing on this material) for the development of graphene‐based materials into a successful technology.
An overview of some recently published work on graphene mechanical properties is presented, and a list of challenges that, notwithstanding the strong hype existing on this material, need to be overcome for large‐scale applications are discussed. Metrology, modeling, processing, and chemical tunability are key challenges to be addressed for the development of graphene‐based materials into a successful technology.
Composite materials with carbon nanotube and graphene additives have long been considered as exciting prospects among nanotechnology applications. However, after nearly two decades of work in the ...area, questions remain about the practical impact of nanotube and graphene composites. This uncertainty stems from factors that include poor load transfer, interfacial engineering, dispersion, and viscosity-related issues that lead to processing challenges in such nanocomposites. Moreover, there has been little effort to identify selection rules for the use of nanotubes or graphene in composite matrices for specific applications. This review is a critical look at the status of composites for developing high-strength, low-density, high-conductivity materials with nanotubes or graphene. An outlook of the different approaches that can lead to practically useful nanotube and graphene composites is presented, pointing out the challenges and opportunities that exist in the field.
Layered two-dimensional (2D) materials such as transition metal dichalcogenides (TMDCs) are receiving increased interest for applications in energy storage due to their high specific surface area and ...versatile electronic structure. In this work, we prepare solvent stabilised dispersions of a variety of few-layer thick TMDC crystals (MoS2, MoSe2, WS2, and TiS2) by ultrasonication. The exfoliated materials were first characterised by a variety of techniques to determine their quality. These dispersions were then used to form supercapacitor electrodes by filtration, without use of any further conductive additives or polymeric binders. These thin layer TMDC electrodes were assembled into symmetrical coin-cell devices for comparative electrochemical testing. It was found that despite being the most widely studied material, MoS2 suffers from inferior charge storage properties compared to the much higher conductivity and lower density TiS2. Impedance spectroscopy was used to investigate the charge storage mechanisms inside the coin cells, which were found to consist of a combination of both rapid, but low magnitude, electric double layer capacitance and much slower, but higher magnitude, ion adsorption pseudocapacitance.
Conventional chemical oxidation routes for the production of graphene oxide (GO), such as the Hummers’ method, suffer from environmental and safety issues due to their use of hazardous and explosive ...chemicals. These issues are addressed by electrochemical oxidation methods, but such approaches typically have a low yield due to inhomogeneous oxidation. Herein we report a two-step electrochemical intercalation and oxidation approach to produce GO on the large laboratory scale (tens of grams) comprising (1) forming a stage 1 graphite intercalation compound (GIC) in concentrated sulfuric acid and (2) oxidizing and exfoliating the stage 1 GIC in an aqueous solution of 0.1 M ammonium sulfate. This two-step approach leads to GO with a high yield (>70 wt %), good quality (>90%, monolayer), and reasonable oxygen content (17.7 at. %). Moreover, the as-produced GO can be subsequently deeply reduced (3.2 at. % oxygen; C/O ratio 30.2) to yield highly conductive (54 600 S m–1) reduced GO. Electrochemical capacitors based on the reduced GO showed an ultrahigh rate capability of up to 10 V s–1 due to this high conductivity.
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