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  • Journal article
    Sokolikova MS, Sherrell PC, Bemmer VL, Mattevi Cet al., 2017,

    Room-temperature growth of colloidal Bi2Te3 nanosheets

    , Chemical Communications, Vol: 53, Pages: 8026-8029, ISSN: 1364-548X

    In this work, we report the colloidal synthesis of Bi2Te3 nanosheets with controlled thickness, morphology and crystallinity at temperatures as low as 20 °C. Grown at room temperature, Bi2Te3 exhibits two-dimensional morphology with thickness of 4 nm and lateral size of 200 nm. Upon increasing the temperature to 170 °C, the nanosheets demonstrate increased thickness of 16 nm and lateral dimensions of 600 nm where polycrystalline nanosheets (20 °C) are replaced by single crystal platelets (170 °C). Rapid synthesis of the material at moderately low temperatures with controllable morphology, crystallinity and consequently electrical and thermal properties can pave the way toward its large-scale production for practical applications.

  • Journal article
    Pesci FM, Sokolikova MS, Grotta C, Sherrell PC, Reale F, Sharda K, Ni N, Palczynski P, Mattevi Cet al., 2017,

    MoS2/WS2 heterojunction for photoelectrochemical water oxidation

    , ACS Catalysis, Vol: 7, Pages: 4990-4998, ISSN: 2155-5435

    The solar-assisted oxidation of water is an essential half reaction for achieving a complete cycle of water splitting. The search of efficient photoanodes that can absorb light in the visible range is of paramount importance to enable cost-effective solar energy-conversion systems. Here, we demonstrate that atomically thin layers of MoS2 and WS2 can oxidize water to O2 under incident light. Thin films of solution-processed MoS2 and WS2 nanosheets display n-type positive photocurrent densities of 0.45 mA cm–2 and O2 evolution under simulated solar irradiation. WS2 is significantly more efficient than MoS2; however, bulk heterojunctions (B-HJs) of MoS2 and WS2 nanosheets results in a 10-fold increase in incident-photon-to-current-efficiency, compared to the individual constituents. This proves that charge carrier lifetime is tailorable in atomically thin crystals by creating heterojunctions of different compositions and architectures. Our results suggest that the MoS2 and WS2 nanosheets and their B-HJ blend are interesting photocatalytic systems for water oxidation, which can be coupled with different reduction processes for solar-fuel production.

  • Journal article
    Riley DJ, Song W, Lischner, Rocha VG, Qin H, Qi J, Hadden JHL, Mattevi, Xie Fet al., 2017,

    Tuning the Double Layer of Graphene Oxide through Phosphorus Doping for Enhanced Supercapacitance

    , ACS Energy Letters, Vol: 2, Pages: 1144-1149, ISSN: 2380-8195

    The electrochemical double layer plays a fundamental role in energy storage applications. Control of the distribution of ions in the double layer at the atomistic scale offers routes to enhanced material functionality and device performance. Here we demonstrate how the addition of an element from the third row of the periodic table, phosphorus, to graphene oxide increases the measured capacitance and present density functional theory calculations that relate the enhanced charge storage to structural changes of the electrochemical double layer. Our results point to how rational design of materials at the atomistic scale can lead to improvements in their performance for energy storage.

  • Journal article
    Amit I, Octon TJ, Townsend NJ, Reale F, Wright CD, Mattevi C, Craciun MF, Russo Set al., 2017,

    Role of charge traps in the performance of atomically-thin transistors

    , Advanced Materials, Vol: 29, ISSN: 1521-4095

    Transient currents in atomically thin MoTe2 field-effect transistors (FETs) are measured during cycles of pulses through the gate electrode. The curves of the transient currents are analyzed in light of a newly proposed model for charge-trapping dynamics that renders a time-dependent change in the threshold voltage as the dominant effect on the channel hysteretic behavior over emission currents from the charge traps. The proposed model is expected to be instrumental in understanding the fundamental physics that governs the performance of atomically thin FETs and is applicable to the entire class of atomically thin-based devices. Hence, the model is vital to the intelligent design of fast and highly efficient optoelectronic devices.

  • Journal article
    Olowojoba GB, Kopsidas S, Eslava S, Saiz Gutierrez E, Kinloch AJ, Mattevi C, Garcia Rocha V, Taylor ACet al., 2017,

    A facile way to produce epoxy nanocomposites having excellent thermal conductivity with low contents of reduced graphene oxide

    , Journal of Materials Science, Vol: 52, Pages: 7323-7344, ISSN: 1573-4803

    A well-dispersed phase of exfoliated graphene oxide (GO) nanosheets was initially prepared in water. This was concentrated by centrifugation and was mixed with a liquid epoxy resin. The remaining water was removed by evaporation, leaving a GO dispersion in epoxy resin. A stoichiometric amount of an anhydride curing agent was added to this epoxy-resin mixture containing the GO nanosheets, which was then cured at 90 °C for 1 hour followed by 160 °C for 2 hours. A second thermal treatment step of 200 °C for 30 minutes was then undertaken to reduce further the GO in-situ in the epoxy nanocomposite. An examination of the morphology of such nanocomposites containing reduced graphene oxide (rGO) revealed that a very good dispersion of rGO was achieved throughout the epoxy polymer. Various thermal and mechanical properties of the epoxy nanocomposites were measured and the most noteworthy finding was a remarkable increase in the thermal conductivity when relatively very low contents of rGO were present. For example, a value of 0.25 W/mK was measured at 30 °C for the nanocomposite with merely 0.06 weight percentage (wt%) of rGO present, which represents an increase of ~40% compared with that of the unmodified epoxy polymer. This value represents one of the largest increases in the thermal conductivity per wt% of added rGO yet reported. These observations have been attributed to the excellent dispersion of rGO achieved in these nanocomposites made via this facile production method. The present results show that it is now possible to tune the properties of an epoxy polymer with a simple and viable method of GO addition.

  • Journal article
    Mattevi C, 2016,

    Graphitic carbon nitride as a catalyst support in fuel cells and electrolyzers

    , Electrochimica Acta, Vol: 222, Pages: 44-57, ISSN: 1873-3859

    Electrochemical power sources, such as polymer electrolyte membrane fuel cells (PEMFCs), require the use of precious metal catalysts which are deposited as nanoparticles onto supports in order to minimize their mass loading and therefore cost. State-of-the-art/commercial supports are based on forms of carbon black. However, carbon supports present disadvantages including corrosion in the operating fuel cell environment and loss of catalyst activity. Here we review recent work examining the potential of different varieties of graphitic carbon nitride (gCN) as catalyst supports, highlighting their likely benefits, as well as the challenges associated with their implementation. The performance of gCN and hybrid gCN-carbon materials as PEMFC electrodes is discussed, as well as their potential for use in alkaline systems and water electrolyzers. We illustrate the discussion with examples taken from our own recent studies.

  • Journal article
    Mansor N, Jia J, Miller TS, Suter T, Jorge AB, Gibbs C, Shearing P, McMillan PF, Mattevi C, Shaffer M, Brett DJLet al., 2016,

    Graphitic carbon nitride-graphene hybrid nanostructure as a catalyst support for polymer electrolyte membrane fuel cells

    , ECS Transactions, Vol: 75, Pages: 885-897, ISSN: 1938-5862

    Graphitic carbon nitrides form a class of semiconducting graphene-like polymeric materials with visible light absorption and photocatalytic properties. In addition to high nitrogen content and tunable structure, it was shown that graphitic carbon nitride based on polytrazine imide (PTI) sheets exhibit excellent anti-corrosion ability in ex-situ fuel cell environments. However, in bulk form, their low surface area and poor conductivity limits their applications in fuel cells. In this work, PTI was exfoliated to form an ink made from single to few-layer nanosheets. The ink was then processed to produce 3D networks of carbon nitride nanosheets/reduced graphene oxide (PTI-rGO) hybrid aerogel with large interconnecting pores for fast mass transport of reactants and high surface area. The material was decorated with platinum nanoparticles, and then investigated for its electrochemical properties and applications as a catalyst support for polymer electrolyte membrane (PEM) fuel cells. Initial results show that the cathode catalytic activity of Pt/rGO-PTI hybrid is significantly improved in comparison to Pt/PTI or Pt/rGO. In addition, the in-situ fuel cell performance of Pt/PTI as anode catalyst is comparable to commercial Pt/C especially at low densities, making it attractive as an alternative, durable anode catalyst support material to conventional carbon black.

  • Journal article
    Pierin G, Grotta C, Colombo P, Mattevi Cet al., 2016,

    Direct Ink Writing of micrometric SiOC ceramic structures using a preceramic polymer

    , Journal of the European Ceramic Society, Vol: 36, Pages: 1589-1594, ISSN: 0955-2219

    © 2016 Elsevier Ltd. In this work we manufactured micro-sized SiOC ceramic components by 3D printing (Direct Ink Writing) of a preceramic polymer. Model porous ceramic scaffolds with the lateral dimension of a few millimeters and composed of a continuous ceramic filament ~120 μm thick were produced, and a suitable rheological behavior was obtained by mixing cross-linked preceramic particles with a siloxane resin dissolved in a solvent. The addition of a low amount (0.025-0.1 wt%) of graphene oxide to the ink formulation further improves the structural stability during pyrolysis reducing the shrinkage of the preceramic polymer. Upon pyrolysis at low temperature (1000 °C), graphene oxide converted into graphene. The resulting scaffolds possess a good compression strength, of ~2.5 MPa for a total porosity of ~64 vol% (~3.1 MPa after the addition of 0.1 wt% graphene oxide).

  • Journal article
    Mattevi C, Yuji Takakuwa YT, 2016,

    Valence-band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics

    , Physica Status Solidi (A) Applied Research, Vol: 213, Pages: 2380-2386, ISSN: 1862-6319

    We report valence-band electronic structure evolution of graphene oxide (GO) upon its thermal reduction. The degree of oxygen functionalization was controlled by annealing temperature, and an electronic structure evolution was monitored using real-time ultraviolet photoelectron spectroscopy. We observed a drastic increase in the density of states around the Fermi level upon thermal annealing at ∼600 °C. The result indicates that while there is an apparent bandgap for GO prior to a thermal reduction, the gap closes after an annealing around that temperature. This trend of bandgap closure was correlated with the electrical, chemical, and structural properties to determine a set of GO material properties that is optimal for optoelectronics. The results revealed that annealing at a temperature of ∼500 °C leads to the desired properties, demonstrated by a uniform and an order of magnitude enhanced photocurrent map of an individual GO sheet compared to an as-synthesized counterpart.

  • Journal article
    Kien-Cuong P, Chang Y-H, McPhail DS, Mattevi C, Wee ATS, Chua DHCet al., 2016,

    Amorphous Molybdenum Sulfide on Graphene-Carbon Nanotube Hybrids as Highly Active Hydrogen Evolution Reaction Catalysts

    , ACS APPLIED MATERIALS & INTERFACES, Vol: 8, Pages: 5961-5971, ISSN: 1944-8244
  • Journal article
    Olowojoba GB, Eslava S, Gutierrez ES, Kinloch AJ, Mattevi C, Rocha VG, Taylor ACet al., 2016,

    In-situ thermally-reduced graphene oxide/epoxy composites: thermal and mechanical properties

    , Applied Nanoscience, Vol: 6, Pages: 1015-1022, ISSN: 2190-5509

    Graphene has excellent mechanical, thermal, optical and electrical properties and this has made it a prime target for use as a filler material in the development of multifunctional polymeric composites. However, several challenges need to be overcome in order to take full advantage of the aforementioned properties of graphene. These include achieving good dispersion and interfacial properties between the graphene filler and the polymeric matrix. In the present work we report the thermal and mechanical properties of reduced graphene oxide/epoxy composites prepared via a facile, scalable and commercially-viable method. Electron micrographs of the composites demonstrate that the reduced graphene oxide (rGO) is well-dispersed throughout the composite. Although no improvements in glass transition temperature, tensile strength, and thermal stability in air of the composites were observed, good improvements in thermal conductivity (about 36%), tensile and storage moduli (more than 13%) were recorded with the addition of 2 wt% of rGO.

  • Journal article
    Reale F, Sharda K, Mattevi C, 2016,

    From bulk crystals to atomically thin layers of group VI-transition metal dichalcogenides vapour phase synthesis

    , Applied Materials Today, Vol: 3, Pages: 11-22, ISSN: 2352-9407

    Traditional synthesis methods of bulk semiconductors developed during the1970s and 1980s have recently undergone a resurgence of research interest. Physical vapour deposition (PVD), chemical vapour deposition (CVD) and metal organic chemical vapour deposition (MOCVD) have been extensively rediscovered to achieve three-atom thick metal dichalcogenides. Often defined as “graphene-analogous materials” atomically thin sulfides and selenides of group VI of transition metals have revealed a plethora of unforeseen optical, electrical and mechanical properties which make them unique candidates for future nanotechnologies, ranging from quantum electronics to large area consumer electronics. In the last few years tremendous progress has been achieved in the synthesis of high quality atomic crystals, often inspired by the consolidated synthesis methodologies of their bulk counterparts. Most interestingly, several of these methods are still used and also implemented to synthesize new compounds, expanding the range of accessible 2D materials. We review this progress and we highlight key difference in the coordination chemistry of different transition metals which are responsible for the different synthesis products.

  • Journal article
    Sherrell PC, Mattevi C, 2016,

    Mesoscale design of multifunctional 3D graphene networks

    , Materials Today, Vol: 19, Pages: 428-436, ISSN: 1873-4103

    Three-dimensional graphene networks are emerging as a new class of multifunctional constructs with a wide range of potential applications from energy storage to bioelectronics. Their multifunctional characteristics stem from the unique combination of mechanical properties, electrical conductivity, ultra-low density, and high specific surface areas which distinguish them from any polymer, ceramic or metal constructs. The most pressing challenge now is the achievement of ordered structures relying on processes that are highly controllable. Recent progresses in materials templating techniques, including the advent of three-dimensional printing, have accelerated the development of macroscopic architectures with micro-level-controlled features by rational design, with potential for manufacturing.

  • Journal article
    Pham KC, McPhail DS, Mattevi C, Wee ATS, Chua DHCet al., 2016,

    Graphene-Carbon Nanotube Hybrids as Robust Catalyst Supports in Proton Exchange Membrane Fuel Cells

    , Journal of the Electrochemical Society, Vol: 163, Pages: F255-F263, ISSN: 0013-4651

    Catalyst degradation is one major challenge preventing the worldwide commercialization of the Proton Exchange Membrane Fuel Cells. In this study, we investigate the development of a novel hierarchical carbonaceous support for the platinum catalysts, called graphene-carbon nanotube hybrids (GCNT), and its degradation behavior during an accelerated degradation test. The carbon support is fabricated by growing graphene directly onto carbon nanotubes to form a unique all-carbon nanostructure possessing both an ultra-high density of exposed graphitic edges of graphene and a porous structure of carbon nanotubes. The GCNT-supported platinum catalyst exhibits a higher intrinsic catalytic activity than a carbon black-supported platinum catalyst, and much higher than a CNT-supported platinum catalyst. The enhanced catalytic activity of the GCNT-supported platinum catalyst is explained by the high graphitic edge density which promotes the catalytic reactions on platinum catalyst. The GCNT-supported platinum catalyst also exhibits a superior electrochemical stability over that of the carbon black-supported platinum catalyst, explained by the high crystallinity of the GCNT support. The superior stability is expressed by a lower loss in polarization performance, a smaller increase in charge transfer resistance, a lower loss in the platinum electrochemical surface area, a lower rate of carbon corrosion, and a more stable catalyst microstructure.

  • Journal article
    Li K, Chong JY, Aba NFD, Wang B, Mattevi Cet al., 2015,

    UV-enhanced sacrificial layer stabilised graphene oxide hollow fibre membranes for nanofiltration

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    Graphene oxide (GO) membranes have demonstrated great potential in gas separation and liquid filtration. For upscale applications, GO membranes in a hollow fibre geometry are of particular interest due to the high-efficiency and easy-assembly features at module level. However, GO membranes were found unstable in dry state on ceramic hollow fibre substrates, mainly due to the drying-related shrinkage, which has limited the applications and post-treatments of GO membranes. We demonstrate here that GO hollow fibre membranes can be stabilised by using a porous poly(methyl methacrylate) (PMMA) sacrificial layer, which creates a space between the hollow fibre substrate and the GO membrane thus allowing stress-free shrinkage. Defect-free GO hollow fibre membrane was successfully determined and the membrane was stable in a long term (1200 hours) gas-tight stability test. Post-treatment of the GO membranes with UV light was also successfully accomplished in air, which induced the creation of controlled microstructural defects in the membrane and increased the roughness factor of the membrane surface. The permeability of the UV-treated GO membranes was greatly enhanced from 0.07 to 2.8 L m-2 h-1 bar-1 for water, and 0.14 to 7.5 L m-2 h-1 bar-1 for acetone, with an unchanged low molecular weight cut off (~250 Da).

  • Journal article
    Ni N, Barg S, Garcia-Tunon E, Macul Perez F, Miranda M, Lu C, Mattevi C, Saiz Eet al., 2015,

    Understanding Mechanical Response of Elastomeric Graphene Networks

    , Scientific Reports, Vol: 5, ISSN: 2045-2322

    Ultra-light porous networks based on nano-carbon materials (such as graphene or carbon nanotubes) have attracted increasing interest owing to their applications in wide fields from bioengineering to electrochemical devices. However, it is often difficult to translate the properties of nanomaterials to bulk three-dimensional networks with a control of their mechanical properties. In this work, we constructed elastomeric graphene porous networks with well-defined structures by freeze casting and thermal reduction, and investigated systematically the effect of key microstructural features. The porous networks made of large reduced graphene oxide flakes (>20 μm) are superelastic and exhibit high energy absorption, showing much enhanced mechanical properties than those with small flakes (<2 μm). A better restoration of the graphitic nature also has a considerable effect. In comparison, microstructural differences, such as the foam architecture or the cell size have smaller or negligible effect on the mechanical response. The recoverability and energy adsorption depend on density with the latter exhibiting a minimum due to the interplay between wall fracture and friction during deformation. These findings suggest that an improvement in the mechanical properties of porous graphene networks significantly depend on the engineering of the graphene flake that controls the property of the cell walls.

  • Journal article
    Aba NFD, Chong JY, Wang B, Mattevi C, Li Ket al., 2015,

    Graphene oxide membranes on ceramic hollow fibers - Microstructural stability and nanofiltration performance

    , JOURNAL OF MEMBRANE SCIENCE, Vol: 484, Pages: 87-94, ISSN: 0376-7388
  • Journal article
    Barg S, Perez FM, Ni N, Pereira PDV, Maher RC, Garcia-Tunon E, Eslava S, Agnoli S, Mattevi C, Saiz Eet al., 2014,

    Mesoscale assembly of chemically modified graphene into complex cellular networks

    , Nature Communications
  • Journal article
    Favaro M, Agnoli S, Di Valentin C, Mattevi C, Cattelan M, Artiglia L, Magnano E, Bondino F, Nappini S, Granozzi Get al., 2014,

    TiO<inf>2</inf>/graphene nanocomposites from the direct reduction of graphene oxide by metal evaporation

    , Carbon, Vol: 68, Pages: 319-329, ISSN: 0008-6223

    We demonstrate that graphene oxide can be efficiently reduced by evaporating metal Titanium in high vacuum. A detailed description of this reaction is provided by combining in situ photoemission spectroscopy measurements and DFT calculations: the titanium atoms readily react with the oxygenated groups of graphene oxide, disrupting the C-O bonds, with the consequent formation of titania and the recovery of the sp2 hybridized carbon atoms. When all surface oxygen is consumed, titanium can react with the carbon substrate and form carbidic species. Resonant photoemission spectroscopy measurements allow identifying the presence and exact energy position in the valence band of the Ti-C and Ti-O-C states, which are supposed to control the electron and energy transfer across the TiO2/graphene interface. Therefore with this study we provide a versatile method and the rationale for controlling, at the atomic level, the nature of the interface of graphene/metal oxide nanocomposites. © 2013 Elsevier Ltd. All rights reserved.

  • Journal article
    Gregory A, Hao L, Klein N, Gallop J, Mattevi C, Shaforost O, Lees K, Clarke Bet al., 2014,

    Spatially resolved electrical characterisation of graphene layers by an evanescent field microwave microscope

    , PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, Vol: 56, Pages: 431-434, ISSN: 1386-9477

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