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Electrowetting is a simple way to induce the spreading and retraction of electrolyte droplets. This method is widely used in “device” applications, where a dielectric layer is applied between the...

Carbon-fibre-reinforced polymer (CFRP) composites are promising materials for non-metallic pipe applications in the oil and gas industry owing to their high corrosion resistance, specific strength and stiffness. However, CFRP has poor gas barrier performance meaning that a liner has to be inserted. Graphene-based nanomaterials have been demonstrated to improve gas barrier properties in thermoplastic polymers, and thus, a CFRP–graphene hybrid composite could provide an alternative to lined pipes. In this work, a method combining spray coating with vacuum-assisted resin infusion was developed to fabricate CFRP hybrid composites with preferred in-plane aligned graphene nanoplatelets. Tensile and flexural properties, as well as CO2 gas permeability, were evaluated. It was illustrated that both tensile and flexural properties performed better under relatively low GNP loadings ( Graphical abstract

Aqueous zinc‐ion hybrid supercapacitors are a promising energy storage technology, owing to their high safety, low cost, and long‐term stability. At present, however, there is a lack of understanding of the potential window and self‐discharge of this aqueous energy storage technology. This study concerns a systematic investigation of the potential window of this device by cyclic voltammetry and galvanostatic charge–discharge. Hybrid supercapacitors based on commercial activated carbon (AC) demonstrate a wide and stable potential window (0.2 V to 1.8 V), high specific capacitances (308 F g−1 at 0.5 A g−1 and 110 F g−1 at 30 A g−1), good cycling stability (10000 cycles with 95.1 % capacitance retention), and a high energy density (104.8 Wh kg−1 at 383.5 W kg−1), based on the active materials. The mechanism involves simultaneous adsorption–desorption of ions on the AC cathode and zinc ion plating/stripping on the Zn anode. This work leads to better understanding of such devices and will aid future development of practical high‐performance aqueous zinc‐ion hybrid supercapacitors based on commercial carbon materials, thus accelerating the deployment of these hybrid supercapacitors and filling the gap between supercapacitors and batteries., A window into self‐discharge: A systematic investigation of the potential window and self‐discharge in aqueous zinc‐ion hybrid supercapacitors based on commercial activated carbon (AC) and Zn foil with nontoxic electrolyte is carried out by cyclic voltammetry and galvanostatic charge–discharge methods, with a view to filling the gap between supercapacitors and batteries.

Most polymers are long-lasting and produced from monomers derived from fossil fuel sources. Bio-based and/or biodegradable plastics have been proposed as a sustainable alternative. Amongst those available, polyhydroxyalkanoate (PHA) shows great potential across a large variety of applications but is currently limited to packaging, cosmetics and tissue engineering due to its relatively poor physical properties. An expansion of its uses can be accomplished by developing nanocomposites where PHAs are used as the polymer matrix. Herein, a PHA biopolyester was melt blended with graphene nanoplatelets (GNPs) or with a 1:1 hybrid mixture of GNPs and carbon nanofibers (CNFs). The resulting nanocomposites exhibited enhanced thermal stability while their Young's modulus roughly doubled compared to pure PHA. The hybrid nanocomposites percolated electrically at lower nanofiller loadings compared to the GNP-PHA system. The electrical conductivity at 15 wt.% loading was ~ 6 times higher than the GNP-based sample. As a result, the electromagnetic interference shielding performance of the hybrid material was around 50% better than the pure GNPs nanocomposites, exhibiting shielding effectiveness above 20 dB, which is the threshold for common commercial applications. The thermal conductivity increased significantly for both types of bio-nanocomposites and reached values around 5 W K-1 m-1 with the hybrid-based material displaying the best performance. Considering the solvent-free and industrially compatible production method, the proposed multifunctional materials are promising to expand the range of application of PHAs and increase the environmental sustainability of the plastic and plastic electronics industry., 26 pages

Poor cycling stability and mechanistic controversies have hindered the wider application of rechargeable aqueous Zn–MnO2 batteries. Herein, direct evidence was provided of the importance of Mn2+ in this type of battery by using a bespoke cell. Without pre‐addition of Mn2+, the cell exhibited an abnormal discharge–charge profile, meaning it functioned as a primary battery. By adjusting the Mn2+ content in the electrolyte, the cell recovered its charging ability through electrodeposition of MnO2. Additionally, a dynamic pH variation was observed during the discharge–charge process, with a precipitation of Zn4(OH)6(SO4)⋅5H2O buffering the pH of the electrolyte. Contrary to the conventional Zn2+ intercalation mechanism, MnO2 was first converted into MnOOH, which reverted to MnO2 through disproportionation, resulting in the dissolution of Mn2+. The charging process occurred by the electrodeposition of MnO2, thus improving the reversibility through the availability of Mn2+ ions in the solution., Taking charge: This work provides direct evidence of the importance of Mn2+ in rechargeable aqueous Zn–MnO2 batteries. The charging process is implemented by the electrodeposition of MnO2, thus improving the reversibility by the availability of Mn2+ in the solution. A conversion reaction between MnO2 and MnOOH occurs, rather than Zn2+ intercalation into MnO2.

A significant challenge for graphene nanoplatelet (GNP) suppliers is the characterisation of platelet morphology in industrial environments. This challenge is further exacerbated to platelet surface chemistry when scalable functionalisation processes, such as plasma treatment, are used to modify the GNPs to improve the filler-matrix interphase in nanocomposites. The costly and complex suite of analytical equipment necessary for a complete material description makes quality control and process optimisation difficult. Raman spectroscopy is a facile and accessible characterisation technique, with recent advancements unlocking fast mapping for rapid data collection. In this study, we develop novel techniques to better characterise GNP morphology and changes in surface chemistry using Raman maps of bulk powders. Providing a bespoke algorithmic framework for the analysis of these advanced materials. An unsupervised peak fitting and processing algorithm was used to extract crystallinity data and correlate it with laser-diffraction-derived lateral size values for a commercial set of GNPs rapidly and accurately. Classical machine learning was used to identify the most informative Raman features for classifying the plasma-functionalised GNPs. The initial material properties were found to affect the peak features that were the most useful for classification. In low defect density and low specific surface area GNPs, the D peak full width at half maximum is found to be the most useful, whereas the I 2D / I G ratio is the most useful in the opposite case. Finally, a convolutional neural network was trained to discern between different GNP grades with 86% accuracy. This work demonstrates how computer vision could be deployed for rapid and accurate quality control on the factory floor.

Transitional metal carbides and nitrides (MXenes) have promise for incorporation into multifunctional composites due to their high electrical conductivity and excellent mechanical and tribological properties. It is unclear, however, to what extent MXenes are also able to improve the mechanical properties of the composites and, if so, what would be the optimal flake size and morphology. Herein, Ti

Graphene oxide (GO) and reduced graphene oxide (rGO) membranes have attracted significant attention as a potential technology for energy storage, gas separation, and water purification applications. However, these membranes have a significant drawback as they became swollen, hence unstable, after exposure to aqueous solutions. Here, we describe membranes produced from graphene prepared by liquid phase exfoliation, possessing a low oxygen content, unlike the GO/rGO systems typically used, and demonstrate their applicability for ion sieving in aqueous solutions. These low oxygen content graphene membranes formed from flakes of varying size were used to determine the effect of flake morphology on ion transport. Interestingly decreasing flake length and thickness leads to an increase in the number and tortuosity of nanochannels between the layers, resulting in a significant reduction of ion transport. The smaller flakes show an increased surface charge, due to the level of defects, which impedes chloride mobility allowing for both physical sieving and charge repulsion. Moreover, the graphene membranes reported here exhibit excellent Na+ rejection properties (∼97%) with water permeance ∼10 times higher than those reported for GO membranes, while demonstrating high stability in aqueous solutions with no observed swelling. These materials are therefore extremely promising for future applications in water purification.

MoS2 and MoO3 have attracted attention due to their interesting properties in energy storage applications, however, the operative charge storage mechanism, whether based on surface ion adsorption and intercalation, is not yet fully understood. In this work, the intercalation of non-hydrated cations into free-standing MoO3-MoS2 electrodes, prepared as composites with graphene, was studied. The oxide material is formed during the solution phase exfoliation process. It is found that tetramethylammonium chloride (TMACl) provides twice the capacitance of tetraethylammonium chloride (TEACl) and tetrapropylammonium chloride (TPACl) solutions. This is attributed to the interlayer spacing of MoS2 (0.615 nm) and MoO3 (0.690 nm), which are greater than the crystallographic diameter of TMA+ (0.558 nm). In contrast, the crystallographic diameter of TEA+ (0.674 nm) and TPA+ (0.758 nm), being larger than the interlayer spacing of MoS2, leads to storage of charge only on the surface of the materials through ion adsorption. Moreover, we have found that use of the TPA+ ion leads to the partial re-exfoliation of the as-prepared materials, which can enhance the capacitance retention during cycling. These results improve the understanding of charge storage mechanism of layered 2D materials.

A green and low-cost method is presented to fabricate graphene fibre electrodes by electrochemical exfoliation of thin strips of graphite foil. When assembled into micro-supercapacitors, the graphene fibres achieved an excellent electrochemical capacitance (∼247.6 mF cm−2 at ∼2 mA cm−2) and low equivalent series resistance (∼2.4 Ω), a significant improvement over the typically used graphene oxide based fibres. This excellent capacitive performance indicates these graphene-based energy storage devices could be ideal for microelectronics applications. Additionally, an all-solid-state flexible micro-supercapacitor was fabricated using a gel electrolyte (H3PO4/PVA) and exhibited a high areal capacitance of 70.6 mF cm−2 and a superior cycling stability of ∼96% capacitance retention after 2400 cycles, suggesting possible applications for flexible energy storage. The easily scalable and facile single step strategy presented here outperforms the conventionally used graphene oxide based methods, which typically require harmful chemicals and involve a more complex synthesis procedure.

A base wash procedure was used to partially remove the oxygen functional groups from the graphene oxide (GO) flakes to prepare the base-washed GO (BwGO). It is found that the base wash treatment does not alter the physical properties (size, thickness etc.) of the GO significantly but the chemical composition is changed. Nanocomposites were prepared by incorporating the BwGO flakes obtained in a poly(vinyl alcohol) (PVA) matrix. It was found the storage modulus of the nanocomposites is enhanced from 4.4 GPa to 6.5 GPa with 5 wt% of BwGO. This is in agreement with the micromechanical estimation obtained by using Raman spectroscopy that follows the interfacial stress transfer from the matrix to the BwGO fillers. The lower effective modulus of BwGO than GO as calculated using the classical ‘rule of mixtures’ is due to the loss of functional groups on GO that serve as a surfactant to prevent the flakes from re-agglomerating. An agglomeration factor ηa is therefore proposed and a concept of ‘effective volume fraction’ is introduced to quantify and evaluate the level of agglomeration of fillers in nanocomposites, which can be otherwise difficult to visualize optically. It is found that the removal of the functional groups causes the flakes to re-agglomerate, and reduces the ‘effective volume fraction’ by about 10–20%.

Organic–inorganic composites show great potential for organic rechargeable lithium-ion batteries. In this work, two-dimensional phthalocyanine molecules were converted into hybrid nanoparticles with a porous structure and bound to a conductive graphene layer to act as a cathode material. The conductivity of this reduced graphene oxide/Fe-phthalocyanine (rGO/FePc) composite is improved through good interfacial connections and internal polymerization. The FePc spheres were shaped with the assistance of Fe3O4 and immobilized between the layers of reduced graphene oxide (rGO). The electrochemical properties of the organic–inorganic composites were investigated by testing in a lithium-ion cell. A high discharge capacity of 186 mAh g−1 was maintained after 100 cycles at 300 mA g−1, which demonstrates a significant improvement in the cycle life compared to previous reports of phthalocyanine-based electrochemical energy storage behaviour.

A systematic study has been undertaken of the reinforcement of poly (vinyl alcohol) (PVA) by hexagonal boron nitride (hBN) nanosheets (BNNSs) produced by the liquid-phase exfoliation of hBN crystals. Three types of BNNSs with different geometries were prepared, two of which had similar lateral dimensions and two that had a similar aspect ratio (length/thickness). PVA nanocomposites with different loadings of the three types of BNNSs were prepared and this enabled the effect of BNNS volume fraction and geometry upon the mechanical properties such as Young's modulus, yield stress and breaking strength, to be determined. Although the Raman scattering from hBN is relatively weak compared with that from graphene, it was shown that Raman spectroscopy could be used to both evaluate the distribution of the BNNSs in the nanocomposites and follow stress transfer from the polymer matrix to the BNNSs. It was found that the reinforcement of the polymer could be modelled using a combinations of the rule of mixtures and modified shear lag theory. The highest level of reinforcement was found for the BNNSs with the largest aspect ratio although there was evidence of a decline in the level of reinforcement at the highest loadings of all types of BNNSs, as the result of agglomeration of the nanosheets.

Safe and low-cost zinc-ion hybrid supercapacitors using neutral aqueous electrolytes are promising for large scale and high power energy storage. A key challenge for Zn-ion hybrid supercapacitors is to increase their energy density without sacrificing the high power performance. Herein, we report a Zn-ion hybrid supercapacitor using a polypyrrole/electrochemical graphene oxide (PPy/EGO) composite cathode and aqueous 1 M ZnCl2 or ZnBr2 electrolytes. The Zn-PPy/EGO system with an operating cell voltage from 0.5 to 1.5 V exhibited high energy and high power densities of 117.7 and 72.1 Wh kg−1 at 0.34 and 12.4 kW kg−1, respectively, outperforming the Zn-ion hybrid supercapacitors using carbon cathodes. This high performance is because of the facilitated electronic and ionic transport in the PPy/EGO composite. In brief, the EGO prepared via the electrochemical method we recently reported has good structure integrity and is easily reduced; the porous PPy/EGO composite from co-electrodeposition benefits fast ion diffusion in pores; the small, monovalent halides anions in the zinc halides electrolytes are highly mobile in bulk PPy for fast solid-phase anion insertion/de-insertion. Electrochemical characterization and ex-situ X-ray photoelectron spectroscopy confirmed the anion-dominated charge storage mechanism of PPy/EGO cathode in Zn-PPy/EGO system.

A green and facile molten-salt (MS) route for the scalable synthesis of free-standing, long-range oriented and corrugated graphene-like sheets from a copper phthalocyanine (CuPc) precursor is reported. Their unique arrangement and transformation behavior in molten potassium chloride (KCl) play a key role in promoting the successful synthesis of the anisotropic nanostrucure.

With the profuse amount of two-dimensional (2D) materials discovered and the improvements in their synthesis and handling, the field of 2D heterostructures has gained increased interest in recent years. Such heterostructures not only overcome the inherent limitations of each of the materials, but also allow the realization of novel properties by their proper combination. The physical and mechanical properties of graphene mean it has a prominent place in the area of 2D heterostructures. In this review, we will discuss the evolution and current state in the synthesis and applications of graphene-based 2D heterostructures. In addition to stacked and in-plane heterostructures with other 2D materials and their potential applications, we will also cover heterostructures realized with lower dimensionality materials, along with intercalation in few-layer graphene as a special case of a heterostructure. Finally, graphene heterostructures produced using liquid phase exfoliation techniques and their applications to energy storage will be reviewed.

Electrically conductive, polymeric materials that maintain their conductivity even when under significant mechanical deformation are needed for actuator electrodes, conformable electromagnetic shielding, stretchable tactile sensors and flexible energy storage. The challenge for these materials is that the percolated, electrically conductive networks tend to separate even at low strains, leading to significant piezoresistance. Herein, deformable conductors were fabricated by spray-coating a nitrile substrate with a graphene-elastomer solution. The coatings showed only slight increase in electrical resistance after thousands of bending cycles and repeated folding-unfolding events. The deformable conductors doubled their electrical resistance at 12% strain and were washable without changing their electrical properties. The conductivity-strain behaviour was modelled by considering the nanofiller separation upon deformation. To boost the conductivity at higher strains, the production process was adapted by stretching the nitrile substrate before spraying, after which it was released. This adaption meant that the electrical resistance doubled at 25 % strain. The electrical resistance was found sufficiently low to give a 1.9 dB/{\mu}m shielding in the 8-12 GHz electromagnetic band. The physical and electrical properties, including the EM screening, of the flexible conductors, were found to deteriorate upon cycling but could be recovered through reheating the coating., Comment: 29 pages, 6 figures

The demand for efficient electrochemical energy storage technology, such as supercapacitors, continues to increase as both the energy and power demands of devices grow. Graphene has attracted wide interest in addressing this energy challenge due to its high conductivity and specific surface area. However, in reality the hydrophobic properties and the restacking of the graphene sheets during device manufacture leads to significantly lower storage performance than that theoretically predicted for isolated sheets. Herein, functionalized graphene was prepared by a convenient one-pot process, where graphene was functionalized with aryl diazonium salts (4-nitrobenzenediazonium tetrafluoroborate (NBD) and 4-bromobenzenediazonium tetrafluoroborate (BBD)) simultaneously during oxidative electrochemical exfoliation of graphite. It was found that the specific capacitance for functionalized graphene was significantly improved compared to pristine graphene due to the introduction of pseudocapacitance by the aryl diazonium salts. The dispersibility of functionalized graphene in water was also found to be improved, implying a better hydrophilicity. NBD functionalized graphene which had been exfoliated/functionalized for a total of 30 minutes exhibited the best energy storage properties with a 5 times increase in specific capacitance (17 mF cm-2) compared to pristine graphene (3 mF cm-2).

Correction for ‘Synthetic 2-D lead tin sulfide nanosheets with tuneable optoelectronic properties from a potentially scalable reaction pathway’ by Kane Norton et al., Chem. Sci., 2019, 10, 1035–1045.

Carbon materials are ubiquitous in energy storage; however, many of the fundamental electrochemical properties of carbons are still not fully understood. In this work, we studied the capacitance of highly ordered pyrolytic graphite (HOPG), with the aim of investigating specific ion effects seen in the capacitance of the basal plane and edge-oriented planes of the material. A series of alkali metal cations, from Li+, Na+, K+, Rb+, and Cs+ with chloride as the counterion, were used at a fixed electrolyte concentration. The basal plane capacitance at a fixed potential relative to the potential of zero charge was found to increase from 4.72 to 9.39 μF cm-2 proceeding down Group 1. In contrast, the edge-orientated samples display capacitance ca. 100 times higher than those of the basal plane, attributed to pseudocapacitance processes associated with the presence of oxygen groups and largely independent of cation identity. This work improves understanding of capacitive properties of carbonaceous materials, leading to their continued development for use in energy storage.

Black phosphorus is a two-dimensional material that has potential applications in energy storage, high frequency electronics and sensing, yet it suffers from instability in oxygenated and/or aqueous systems. Here we present the use of a polymeric stabilizer which prevents the degradation of nearly 68% of the material in aqueous media over the course of ca. 1 month.

Two-dimensional crystals are promising building blocks for the new generation of energy materials due to their low volume, high surface area, and high transparency. Electrochemical behavior of these crystals determines their performance in applications such as energy storage/conversion, sensing, and catalysis. Nevertheless, the electrochemistry of an isolated monolayer of molybdenum disulfide, which is one of the most promising semiconducting crystals, has not been achieved to date. We report here on photoelectrochemical properties of pristine monolayer and few-layer basal plane MoS2, namely the electron transfer kinetics and electric double-layer capacitance, supported by an extensive physical and chemical characterization. This enables a comparative qualitative correlation among the electrochemical data, MoS2 structure, and external illumination, although the absolute magnitudes of the electron transfer and capacitance are specific to the redox mediator and electrolyte used in these measurements ([Ru(NH3)6]3+/2+ and LiCl, respectively). Our work shows a strong dependence of the electrochemical properties on the number of MoS2 layers and illumination intensity and proves that an effective interlayer charge transport occurs in bulk MoS2. This highlights the exciting opportunities for tuning of the electrochemical performance of MoS2 through modification of its structure, external environment, and illumination.

A new wet chemistry approach, based on the hot-injection–thermolytic decomposition of the single-source precursor [Mo2O2S2(S2COEt)2] in oleylamine, is described for the production of nanodimensional 1H-MoS2@oleylamine. High quality freestanding MoS2 nanosheets capped with oleylamine have been prepared and subjected to detailed compositional analyses for the first time. The selection of the appropriate reaction temperatures (200–325 °C) in the simple yet robust procedure allows control of the lateral nanosheet dimensions which range from 4.5 to 11.5 nm, as 1H-MoS2@oleylamine entities which maintain a consistent chemical composition (MoS2·oleylamine0.28–0.33). This work provides the first example of atomic resolution STEM imaging of these fine-scale nanosheet materials, providing new insights into their morphology and demonstrating that those freestanding MoS2 nanosheets are pure, highly crystalline, randomly oriented monolayers. The 1H-MoS2@oleylamine samples were analyzed by attenuated total reflectance F...

We demonstrate the controlled tuning of the electronic band structure of large-arrays of graphene nanoribbons (GNRs) by chemical functionalization. The GNR arrays are synthesized by substrate-controlled metal-assisted etching of graphene in H2 at high temperature, and functionalized with different molecules. From Raman spectroscopy and carrier transport measurements, we found that 4-nitrobenzenediazonium (4-NBD) and diethylene triamine (DETA) molecules can tune the doping level of the GNR arrays to p- and n-type, respectively. In both cases, the doping effects induced in the GNRs were found to be higher than for a pristine graphene sheet, due to the presence of a large quantity of edges. Effects of chemical doping on the Raman spectrum of sp(2) carbon materials are also discussed. Our findings offer an effective way to control the electronic structure of GNRs by chemical functionalization, and are expected to facilitate the production of nanoribbon-based p-n junctions for future implementation into electronic circuits.

Laminar membranes of two-dimensional materials are excellent candidates for applications in water filtration due to the formation of nanocapillaries between individual crystals that can exhibit a molecular and ionic sieving effect, while allowing high water flux. This approach has been exemplified previously with graphene oxide, however these membranes suffer from swelling when exposed to liquid water, leading to low salt rejection and reducing their applicability for desalination applications. Here, we demonstrate that by producing thin (∼5 μm) laminar membranes of exfoliated molybdenum disulfide (MoS

Chemical functionalisation is a promising method to tune the electronic structure of graphene, and the two-dimensional structure of graphene enables access to both of its faces for various types of functionalisation. Here, we present the effect of covalent functionalisation on the Raman spectrum in terms of monofacial (one-sided) and bifacial (two-sided) functionalisation using both monolayer and bilayer graphene. Asymmetrical or ‘Janus’ functionalisation is found to provide significantly increased levels of doping compared to other schemes allowing for control over graphene's electronic structure as well as control over surface functionality.

Chemical functionalization and mechanical strain of graphene are both important for the optimization of flexible electronic devices as both can alter the electronic structure of graphene. Here, we investigate the combined effects of covalent aryl diazonium functionalization and mechanical strain on graphene by Raman spectroscopy. Raman spectroscopy provides a wealth of information regarding the electronic structure of graphene and can be easily applied to flexible device architectures. The use of chemical vapor deposition (CVD) grown polycrystalline graphene is found to exhibit increased reactivity toward diazonium functionalization. This is attributed to the increased reactivity of defects predominantly present along domain boundaries. Functionalization with nitrobenzene diazonium molecules causes p-type doping to occur in the CVD graphene. The combined effects of mechanical strain and chemical functionalization on the graphene are also investigated. The Raman peak width is affected because of phonon spl...

Using a conventional Raman experimental apparatus, we demonstrate that the photoluminescent (PL) yield from ultrasonication-exfoliated transition metal dichalcogenides (TMDs) (MoS2 and WS2) can be increased by up to 8-fold by means of a laser etching procedure. This laser etching process allows us to controllably pattern and reduce the number of layers of the solution-exfoliated material, overcoming the key drawback to solvent-based exfoliation of two-dimensional (2D) semiconducting materials for applications in optoelectronics. The successful laser thinning of the exfoliated 2D crystals was investigated systematically by changes in both Raman and PL spectra. A simple proof-of-principle of the scalability of this laser etching technique for solution-exfoliated TMD crystals was also demonstrated. As well as being applicable for individual materials, it is also possible to use this simple laser etching technique to investigate the structure of solution-generated van der Waals heterostructures, consisting of layers of both MoS2 and WS2.

Substrates with four different nanotube modifications have been prepared and their electron transport properties measured. Two modification techniques were compared; covalent chemical attachment of both single and multi-walled carbon nanotubes to transparent conductive (fluorine doped tin oxide) glass surfaces and chemical vapour deposition (CVD) growth of both single and multi-walled carbon nanotubes on highly doped conductive silicon wafers. These carbon nanotube modified substrates were investigated using scanning electron microscopy and substrates with nanotubes grown via CVD have a much higher density of nanotubes than substrates prepared using chemical attachment. Raman spectroscopy was used to verify that nanotube growth or attachment was successful. The covalent chemical attachment of nanotubes was found to increase substrate electron transfer substantially compared to that observed for the bare substrate. Nanotube growth also enhanced substrate conductivity but the effect is smaller than that observed for covalent attachment, despite a lower nanotube density in the attachment case. In both modification techniques, attachment and growth, single-walled carbon nanotubes were found to have superior electron transfer properties. Finally, solar cells were constructed from the nanotube modified substrates and the photoresponse from the different substrates was compared showing that chemically attached single-walled nanotubes led to the highest power generation. © 2012 Elsevier Ltd. All rights reserved. Refereed/Peer-reviewed

Electrically conductive composites comprising polymers and graphene are extremely versatile and have a wide range of potential applications. The conductivity of these composites depends on the choice of polymer matrix, the type of graphene filler, the processing methodology, and any post-production treatments. In this review, we discuss the progress in graphene-polymer composites for electrical applications. Graphene filler types are reviewed, the progress in modelling these composites is outlined, the current optimal composites are presented, and the example of strain sensors is used to demonstrate their application.

The polarizable organic/water interface is used to construct MoS

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.

Here, we evaluate the electrochemical performance of sparsely studied natural crystals of molybdenite and graphite, which have increasingly been used for fabrication of next generation monolayer molybdenum disulphide and graphene energy storage devices. Heterogeneous electron transfer kinetics of several redox mediators, including Fe(CN)6(3-/4-), Ru(NH3)6(3+/2+) and IrCl6(2-/3-) are determined using voltammetry in a micro-droplet cell. The kinetics on both materials are studied as a function of surface defectiveness, surface ageing, applied potential and illumination. We find that the basal planes of both natural MoS2 and graphite show significant electroactivity, but a large decrease in electron transfer kinetics is observed on atmosphere-aged surfaces in comparison to in situ freshly cleaved surfaces of both materials. This is attributed to surface oxidation and adsorption of airborne contaminants at the surface exposed to an ambient environment. In contrast to semimetallic graphite, the electrode kinetics on semiconducting MoS2 are strongly dependent on the surface illumination and applied potential. Furthermore, while visibly present defects/cracks do not significantly affect the response of graphite, the kinetics on MoS2 systematically accelerate with small increase in disorder. These findings have direct implications for use of MoS2 and graphene/graphite as electrode materials in electrochemistry-related applications.

Graphene has been widely studied for its many extraordinary properties, and other two-dimensional layered materials are now gaining increased interest. These excellent properties make thin layer materials very attractive for integration into a wide variety of technologies, particularly in flexible optoelectronic devices. Therefore, gaining control over these properties will allow for a more focused design and optimisation of these possible technologies. Through the application of mechanical strain it is possible to alter the electronic structures of two-dimensional crystals, such as graphene and transition metal dichalcogenides (e.g. MoS2), and these changes in electronic structure can alter their behaviour. In this perspective we discuss recent advances in the strain engineering of thin layer materials, with a focus on using Raman spectroscopy and electrical transport to investigate the effect of strain as well as the effect of strain on the chemical functionalisation of graphene.

Large hexagonal single-crystalline domains of single-layer graphene are epitaxially grown by ambient-pressure chemical vapor deposition over a thin Cu(111) film deposited on c-plane sapphire. The hexagonal graphene domains with a maximum size of 100 µm are oriented in the same direction due to the epitaxial growth. Reflecting high crystallinity, a clear band structure with the Dirac cone is observed by angle-resolved photoelectron spectroscopy (ARPES), and a high carrier mobility exceeding 4,000 cm2 V-1 s-1 is obtained on SiO2/Si at room temperature. Our epitaxial approach combined with large domain growth is expected to contribute to future electronic applications.

We investigate the effect of mechanical strain on graphene synthesized by chemical vapor deposition (CVD) transferred onto flexible polymer substrates by observing the change in the Raman spectrum and then compare this to the behavior of exfoliated graphene. Previous studies into the effect of strain on graphene have focused on mechanically exfoliated graphene, which consists of large single domains. However, for wide scale applications CVD produced films are more applicable, and these differ in morphology, instead consisting of a patchwork of smaller domains separated by domain boundaries. We find that under strain the Raman spectra of CVD graphene transferred onto a silicone elastomer exhibits unusual behavior, with the G and 2D band frequencies decreasing and increasing respectively with applied strain. This unusual Raman behavior is attributed to the presence of domain boundaries in polycrystalline graphene causing unexpected shifts in the electronic structure. This was confirmed by the lack of such behavior in mechanically exfoliated large domain graphene and also in large single-crystal graphene domains grown by CVD. Theoretical calculation of G band for a given large shear strain may explain the unexpected shifts while the shift of the Dirac points from the K point explain the conventional behavior of a 2D band under the strain.