Suchergebnisse

Lithium ion batteries (LIBs) are the enabling technology for many of the societal changes that are expected to happen in the following years. Among all the challenges for which LIBs are the key, vehicle electrification is one of the most crucial. Current battery materials cannot provide the required power densities for such applications and therefore, it makes necessary to develop new materials. Silicon is one of the proposed as next generation battery materials, but still there are challenges to overcome. Poor capacity retention is one of those drawbacks, and because it is tightly related with its high capacity, it is a problem rather difficult to address with common and scalable fabrication processes. Here we show that combining 0D and 1D silicon nanostructures, high capacity and stability can be achieved even using standard electrode fabrication processes. Capacities as high as 1200 mAh/g for more than 500 cycles at high current densities (2 A/g) were achieved with the produced hybrid 0D/1D electrodes. In this research, it was shown that while 0D nanostructures provide good strain relaxation capabilities, 1D nanomaterials contribute with enhanced cohesion and conductive matrix integrity ; This research was funded by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 713567 and Science Foundation Irelands Research Centre award 12/RC/2278_P2. This work was supported by the Ministerio de Economía y Competitividad (MINECO) of Spain, under Grant ENE2014-57977-C2-1-R and "Estancias de Movilidad Salvador Madariaga". Financial support from the U.S. Department of Defense (grant W911NF-14-1-0046), and from the U.S. Department of Energy, through the Consortium for Integrating Energy Systems in Engineering and Science Education, CIESESE (DE-NA0003330) is also acknowledged

PUBLISHED ; Export Date: 15 September 2016 ; Here we demonstrate that liquid phase exfoliation can be used to convert layered crystals of nickel hydroxide into Ni(OH)2 nanosheets in relatively large quantities and without the need for ion intercalation. While other procedures require harsh synthesis conditions and multiple reaction steps, this method involves ultrasonication of commercially available powders in aqueous surfactant solutions and so is relatively mild and potentially scalable. Such mild exfoliation is possible because the surface energy of Ni(OH)2, as measured by inverse gas chromatography, is relatively low at ?70 mJ m?2, similar to other layered materials. TEM, AFM, XPS and Raman spectroscopy show the exfoliated nanosheets to be relatively thin (mean ?10 monolayers thick) and of good quality. Size selection by liquid cascade centrifugation allowed the production of samples with mean nanosheet lengths ranging from 55 to 195 nm. Optical measurements on dispersions showed the optical absorption coefficient spectra to be relatively invariant with nanosheet size while the scattering coefficient spectra varied strongly with size. The resultant size-dependence allows the extinction spectra to be used to estimate nanosheet size as well as concentration. We used the exfoliated nanosheets to prepare thin film electrodes for use in supercapacitors and as oxygen evolution catalysts. While the resultant capacitance was reasonably high at ?1200 F cm?3 (20 mV s?1), the catalytic performance was exceptional with currents of 10 mA cm?2 observed at overpotentials as low as 297 mV, close to the state of the art. ; This work was primarily funded by Science Foundation Ireland through the PI program (11/PI/1087). The research leading to these results has also received funding from the European Union Seventh Framework Program under grant agreement no. 604391 Graphene Flagship, the European Research Council (SEMANTICS) and the Science Foundation Ireland (SFI) funded centre AMBER (SFI/12/RC/2278)

PUBLISHED ; Export Date: 5 August 2015 ; Here we demonstrate the production of large quantities of gallium sulfide (GaS) nanosheets by liquid exfoliation of layered GaS powder. The exfoliation was achieved by sonication of the powder in suitable solvents. The variation of dispersed concentration with solvent was consistent with classical solution thermodynamics and showed successful solvents to be those with Hildebrand solubility parameters close to 21.5 MPa1/2. In this way, nanosheets could be produced at concentrations of up to ~0.2 mg/ml with lateral sizes and thicknesses of 50-1000 nm and 3-80 layers, respectively. The nanosheets appeared to be relatively defect free although oxygen was observed in the vicinity of the edges. Using controlled centrifugation techniques, it was possible to prepare dispersions containing size-selected nanosheets. Spectroscopic measurements showed the optical properties of the dispersions to vary strongly with nanosheet size, allowing the elucidation of spectroscopic metrics for in-situ estimation of nanosheet size and thickness. These techniques allow the production of nanosheets with controlled sizes which will be important for certain applications. To demonstrate this, we prepared films of GaS nanosheets of three different sizes for use as hydrogen evolution electrocatalysts. We found a clear correlation between performance and size showing small nanosheets to be more effective. This is consistent with the catalytically active sites residing on the nanosheet edges. ; The research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement n°604391 Graphene Flagship. We have also received support from the Science Foundation Ireland (SFI) funded centre AMBER (SFI/12/RC/2278). In addition, JNC acknowledges the European Research Council (SEMANTICS) and SFI (11/PI/1087) for financial support. CB acknowledges the German research foundation DFG (BA 4856/1-1). HCN, EMcG, AS-A and VN acknowledge ERC 2DNanoCaps, SFI PIYRA and FP7 MoWSeS. GSD, NCB and SW acknowledge SFI for PI_10/IN.1/I3030. NMcE acknowledges SFI (14/TIDA/2329). STEM experiments were performed at SuperSTEM, the EPSRC UK national facility for aberration-corrected STEM.

PUBLISHED ; cited by 1 ; Two-dimensional nanomaterials such as MoS2 are of great interest both because of their novel physical properties and their applications potential. Liquid exfoliation, an important production method, is limited by our inability to quickly and easily measure nanosheet size, thickness or concentration. Herein, we demonstrate a method to simultaneously determine mean values of these properties from an optical extinction spectrum measured on a liquid dispersion of MoS2 nanosheets. The concentration measurement is based on the size-independence of the low-wavelength scattering coefficient while the size and thickness measurements rely on the effect on edges and quantum confinement on the optical spectra. The resultant controllability of concentration, size and thickness facilitates the preparation of dispersions with pre-determined properties such as high monolayer-content, leading to first measurement of direct-gap MoS2 luminescence in liquid suspensions. These techniques are general and can be applied to a range of 2-dimensional materials including WS2, MoSe2 and WSe2. ; The research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement n°604391 Graphene Flagship. In addition, JNC acknowledges the European Research Council grant SEMANTICS and the SFI grant number 17 11/PI/1087 for financial support. CB acknowledges the German research foundation DFG (BA 4856/1-1). NS and JM acknowledge support from DFG SPP 1459 (MA 4079/7-1) and European Research Council (grant number 259286). GSD and NB acknowledge SFI for PI_10/IN.1/I3030. NMcE thanks FP7-2010-PPP Green Cars Electrograph (266391).

This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/nn500767b. ; We demonstrate wide-band ultrafast optical pulse generation at 1, 1.5, and 2 μm using a single-polymer composite saturable absorber based on double-wall carbon nanotubes (DWNTs). The freestanding optical quality polymer composite is prepared from nanotubes dispersed in water with poly(vinyl alcohol) as the host matrix. The composite is then integrated into ytterbium-, erbium-, and thulium-doped fiber laser cavities. Using this single DWNT-polymer composite, we achieve 4.85 ps, 532 fs, and 1.6 ps mode-locked pulses at 1066, 1559, and 1883 nm, respectively, highlighting the potential of DWNTs for wide-band ultrafast photonics. ; We acknowledge funding from EPSRC GR/ S97613/01, EP/E500935/1, the ERC Grant NANOPOTS, a Royal Society Brian Mercer Award for Innovation. A.C.F. is a Royal Society Wolfson Research Merit Award holder. V.N. wishes to acknowledge support from the European Research Council (ERC Starting Grant 2DNanoCaps) and Science Foundation Ireland, P.T. from National Natural Science Foundation of China, Grants No. 11225421, F.B. from the Newton International Fellowship, Z.S. from Teknologiateollisuus TT-100, the European Union's Seventh Framework Programme (No. 631610), and Aalto University, T.H. from NSFC (Grant No. 61150110487), and the Royal Academy of Engineering (Graphlex).

5 Figuras.- Información complementaria disponible en línea en la página web del editor ; Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorphous carbon nanoparticles into porous nanostructures. We report the use of a pulsed infrared laser to prepare CNF from a graphene oxide (GO) target material. Electron microscopy shows that the films consist of dendritic strings that form web-like three-dimensional structures. The conductivity of these structures can be modified by using the CNF as a nanostructured scaffold for gold nanoparticles deposited by sputter coating, controllably increasing the conductivity by up to 4 orders of magnitude. The ability to measure the conductivity of the porous structures allows electrochemical measurements in the environment. Upon decreasing humidity, the pristine CNF exhibits an increase in resistance with a quick response and recovery time. By contrast, the gold-sputtered CNF showed a decrease in resistance, indicating modification of the doping mechanism due to water adsorption. The sensitivity to humidity is eliminated at the percolation threshold of the metal on the CNF. ; Graham Booth's work is highly appreciated, helping to set up the deposition system. This work has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement 642742 as well as from EU H2020 program "Graphene Flagship" (Grant Agreement 696656). R.A. gratefully acknowledges the support from the Spanish Ministerio de Economia y Competitividad (Grant MAT2016-79776-P, (AEI/FEDER, UE)), from the Government of Aragon and the European Social Fund under the project "Construyendo Europa desde Aragon" 2014–2020 (Grant E/26). A.M.B and W.K.M gratefully acknowledge the financial support from Spanish MINECO and AEI (Project ENE2016-79282-C5-1-R and associated EU Regional Development Funds) and the Gobierno de Aragón (Consolidated Group DGA-T66-GCNN and associated EU Social Funds). S.V.-R. thanks Spanish MINECO for her Ph.D. grant (BES2014-068727 and associated EU Social Funds). ; Peer reviewed

5 Figuras.- Información complementaria disponible en línea en la página web del editor ; Carbon nanofoam (CNF) is a low-density, high-surface-area material formed by aggregation of amorphous carbon nanoparticles into porous nanostructures. We report the use of a pulsed infrared laser to prepare CNF from a graphene oxide (GO) target material. Electron microscopy shows that the films consist of dendritic strings which form web-like three-dimensional structures. The conductivity of these structures can be modified by using the CNF as a nanostructured scaffold for gold nanoparticles deposited by sputter coating, controllably increasing the conductivity by up to four orders of magnitude. The ability to measure the conductivity of the porous structures allows electrochemical measurements in the environment. Upon decreasing humidity, the pristine CNF exhibits an increase in resistance with a quick response and recovery time. By contrast, the gold-sputtered CNF showed a decrease in resistance, indicating modification of the doping mechanism due to water adsorption. The sensitivity to humidity is eliminated at the percolation threshold of the metal on the CNF. ; Graham Booth's work is highly appreciated helping to set up the deposition system. This work has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 642742 as well as for EU H2020 program "Graphene Flagship" (Grant Agreement 696656). R.A. gratefully acknowledges the support from the Spanish Ministerio de Economia y Competitividad (MAT2016-79776-P, (AEI/FEDER, UE)), from the Government of Aragon and the European Social Fund under the project "Construyendo Europa desde Aragon" 2014-2020 (grant number E/26). A.M.B and W.K.M gratefully acknowledge the financial support from Spanish MINECO and AEI (project ENE2016-79282-C5-1-R and associated EU Regional Development Funds), and the Gobierno de Aragón (Consolidated Group DGA-T66-GCNN and associated EU Social Funds). SVR thanks Spanish MINECO for her PhD grant (BES2014-068727 and associated EU Social Funds). ; Peer reviewed