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Laffont L.,CNRS Inter-university Material Research and Engineering | Gibot P.,CNRS Laboratory of Chemistry and Reactivity of Solids
Materials Characterization | Year: 2010

Manganese oxides particularly Mn3O4 Hausmannite are currently used in many industrial applications such as catalysis, magnetism, electrochemistry or air contamination. The downsizing of the particle size of such material permits an improvement of its intrinsic properties and a consequent increase in its performances compared to a classical micron-sized material. Here, we report a novel synthesis of hydrophilic nano-sized Mn 3O4, a bivalent oxide, for which a precise characterization is necessary and for which the determination of the valency proves to be essential. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and particularly High Resolution Electron Energy Loss Spectroscopy (HREELS) allow us to perform these measurements on the nanometer scale. Well crystallized 10-20 nm sized Mn3O4 particles with sphere-shaped morphology were thus successfully synthesized. Meticulous EELS investigations allowed the determination of a Mn3+/Mn 2+ ratio of 1.5, i.e. slightly lower than the theoretical value of 2 for the bulk Hausmannite manganese oxide. This result emphasizes the presence of vacancies on the tetrahedral sites in the structure of the as-synthesized nanomaterial. © 2010 Elsevier Inc.

Pech D.,Roche Holding AG | Pech D.,Toulouse 1 University Capitole | Brunet M.,Roche Holding AG | Brunet M.,Toulouse 1 University Capitole | And 9 more authors.
Nature Nanotechnology | Year: 2010

Electrochemical capacitors, also called supercapacitors, store energy in two closely spaced layers with opposing charges, and are used to power hybrid electric vehicles, portable electronic equipment and other devices. By offering fast charging and discharging rates, and the ability to sustain millions of cycles, electrochemical capacitors bridge the gap between batteries, which offer high energy densities but are slow, and conventional electrolytic capacitors, which are fast but have low energy densities. Here, we demonstrate microsupercapacitors with powers per volume that are comparable to electrolytic capacitors, capacitances that are four orders of magnitude higher, and energies per volume that are an order of magnitude higher. We also measured discharge rates of up to 200 V s -1, which is three orders of magnitude higher than conventional supercapacitors. The microsupercapacitors are produced by the electrophoretic deposition of a several-micrometre-thick layer of nanostructured carbon onions with diameters of 67 nm. Integration of these nanoparticles in a microdevice with a high surface-to-volume ratio, without the use of organic binders and polymer separators, improves performance because of the ease with which ions can access the active material. Increasing the energy density and discharge rates of supercapacitors will enable them to compete with batteries and conventional electrolytic capacitors in a number of applications. © 2010 Macmillan Publishers Limited. All rights reserved.

Merlet C.,University Pierre and Marie Curie | Merlet C.,CNRS RS2E | Rotenberg B.,University Pierre and Marie Curie | Rotenberg B.,CNRS RS2E | And 9 more authors.
Nature Materials | Year: 2012

Lightweight, low-cost supercapacitors with the capability of rapidly storing a large amount of electrical energy can contribute to meeting continuous energy demands and effectively levelling the cyclic nature of renewable energy sources. The excellent electrochemical performance of supercapacitors is due to a reversible ion adsorption in porous carbon electrodes. Recently, it was demonstrated that ions from the electrolyte could enter sub nanometre pores, greatly increasing the capacitance. However, the molecular mechanism of this enhancement remains poorly understood. Here we provide the first quantitative picture of the structure of an ionic liquid adsorbed inside realistically modelled microporous carbon electrodes. We show how the separation of the positive and negative ions occurs inside the porous disordered carbons, yielding much higher capacitance values (125 F g -1) than with simpler electrode geometries. The proposed mechanism opens the door for the design of materials with improved energy storage capabilities. It also sheds new light on situations where ion adsorption in porous structures or membranes plays a role. © 2012 Macmillan Publishers Limited. All rights reserved.

Connetable D.,CNRS Inter-university Material Research and Engineering | Thomas O.,Aix - Marseille University | Thomas O.,CNRS Institute Materials Microelectronics nanosciences of Provence
Journal of Alloys and Compounds | Year: 2011

We present a study of nickel-silicides ordered alloys by means of first-principles calculations. Emphasis was put on the phases (low and high temperatures) identified in the binary phase diagram, namely: Ni 3Si-β1, -β2, and -β3, Ni31Si12-γ, Ni2Si-δ, -θ, Ni3Si2-ε, NiSi-MnP and NiSi2-α. In addition, some common structures are computed for information: L12, D03 and D022. The simulations reproduce with a high accuracy lattice parameters and formation energies of main experimental structures, except for β2 and β3. Our results clarify the crystallographic nature of the γ structure, and the comparison of experimental Raman spectra and vibrational calculations will help experimentalists to identify without ambiguity NiSi3 structures. © 2010 Elsevier B.V. All rights reserved.

Billaud J.,University of St. Andrews | Clement R.J.,University of Cambridge | Armstrong A.R.,University of St. Andrews | Canales-Vazquez J.,University of Castilla - La Mancha | And 3 more authors.
Journal of the American Chemical Society | Year: 2014

There is much interest in Na-ion batteries for grid storage because of the lower projected cost compared with Li-ion. Identifying Earth-abundant, low-cost, and safe materials that can function as intercalation cathodes in Na-ion batteries is an important challenge facing the field. Here we investigate such a material, β-NaMnO2, with a different structure from that of NaMnO2 polymorphs and other compounds studied extensively in the past. It exhibits a high capacity (of ca. 190 mA h g-1 at a rate of C/20), along with a good rate capability (142 mA h g-1 at a rate of 2C) and a good capacity retention (100 mA h g-1after 100 Na extraction/insertion cycles at a rate of 2C). Powder XRD, HRTEM, and 23Na NMR studies revealed that this compound exhibits a complex structure consisting of intergrown regions of NaMnO2 and β-NaMnO2 domains. The collapse of the long-range structure at low Na content is expected to compromise the reversibility of the Na extraction and insertion processes occurring upon charge and discharge of the cathode material, respectively. Yet stable, reproducible, and reversible Na intercalation is observed. © 2014 American Chemical Society.

Simon P.,CNRS Inter-university Material Research and Engineering | Gogotsi Y.,Drexel University
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2010

Electrochemical capacitors, also known as supercapacitors, are energy storage devices that fill the gap between batteries and dielectric capacitors. Thanks to their unique features, they have a key role to play in energy storage and harvesting, acting as a complement to or even a replacement of batteries which has already been achieved in various applications. One of the challenges in the supercapacitor area is to increase their energy density. Some recent discoveries regarding ion adsorption in microporous carbon exhibiting pores in the nanometre range can help in designing the next generation of high-energy-density supercapacitors. © 2010 The Royal Society.

Drouet C.,CNRS Inter-university Material Research and Engineering
Journal of Chemical Thermodynamics | Year: 2015

Apatites are minerals encountered in many fields including geochemistry, nuclear and environmental sciences as well as medicine. This ubiquity is likely related to the diversity of ion substitutions that the apatite structure can accommodate, making of it an excellent "ion reservoir" either in natural settings or for the intentional production of doped systems with tailored properties. Despite this widespread interest for apatite compounds, however, only few studies are dedicated to study their thermodynamic properties. Yet, their knowledge becomes necessary for assessing stability domains and understanding evolutionary trends in solution or upon heating, for example. Recently, the experimental thermodynamics of 33 phosphate apatite compounds (deriving from the composition M10(PO4)6X2) have been reviewed and their comparison allowed the development of the additive predictive model "ThermAP" (Applied Predictive Thermodynamics) capable of adequately predicting properties such as standard enthalpies (δHf{ring operator}), Gibbs free energies of formation (δGf{ring operator}), or entropies (S°) at T =298K, for any composition involving ions among M2+ =Ca2+, Ba2+, Sr2+, Mg2+, Cd2+, Pb2+, Cu2+, Zn2+ and X- =OH-, F-, Cl- or Br-. Although experimental data for apatites involving other divalent cations such as Ni2+, Co2+, Mn2+ or Fe2+ do not seem to be available, the exploration of apatites doped with these ions is appealing from a practical and fundamental viewpoint, for example for understanding geochemical events, or when using apatite precipitation for the elimination of metal cations from industrial wastewaters, or else for conferring magnetic properties to apatite systems in medicine. Based on multiple physico-chemical correlations, the present contribution extends the additive predictive model ThermAP to Ni-, Co-, Mn(II)- and Fe(II)-doped apatites. It provides for the first time estimations of enthalpies, Gibbs free energies of formation and entropies, unveiling the general stability ranking Mn(II)-apatite>Fe(II)-apatite>Co-apatite≥Ni-apatite. This additive approach also allows one to estimate these properties for any composition in view of enabling thermodynamic calculations for applicative or fundamental purposes. © 2015 Elsevier Ltd.

Connetable D.,CNRS Inter-university Material Research and Engineering
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present first-principles calculations of carbon and silicon chiral framework structures (CFSs). In this system, proposed recently by Pickard and Needs [Phys. Rev. BPRLTAO1098-012110.1103/PhysRevB.81.014106 81, 014106 (2010)], atoms form only pentagonal cycles. This configuration enables unambiguous analysis of the effects of pentagons on electronic, vibrational, and thermodynamic properties. The local density approximation electronic band gaps in CFSs were found to be equal to or greater than those of clathrates using the same formalism, as confirmed by GW calculations: 1.8 and 5.5 eV for Si and C-CFS, respectively. We show that, as in clathrates, an increasing electronic band gap is correlated with the contraction of the valence bands, resulting from the frustration of the p shells. The electron localized function and Wannier analysis confirm the sp3 nature of the bonds. Finally, we discuss vibrational and related properties. We show that CFSs present singularities, in particular, that the higher frequencies are not located at the Γ point. © 2011 American Physical Society.

Cazalbou S.,CNRS Inter-university Material Research and Engineering | Bertrand G.,CNRS Inter-university Material Research and Engineering | Drouet C.,CNRS Inter-university Material Research and Engineering
Journal of Physical Chemistry B | Year: 2015

Biomimetic apatites are appealing compounds for the elaboration of bioactive bone-repair scaffolds due to their intrinsic similarity to bone mineral. Bone surgeries are however often heavy procedures, and the infiltration of pathogens may not be totally avoided. To prevent their development, systemic antibiotic prophylaxis is widespread but does not specifically target surgical sites and involves doses not always optimized. A relevant alternative is a preliminary functionalization by an infection-fighting agent. In this work, we investigated from a physicochemical viewpoint the association of a wide-spectrum antibiotic, tetracycline (TC), and a biomimetic nanocrystalline apatite previously characterized. TC adsorption kinetics and isotherm were thoroughly explored. Kinetic data were fitted to various models (pseudo-first-order, pseudo-second-order, general kinetic model of order n, Elovich, double-exponential, and purely diffusive models). The best fit was found for a double-exponential kinetic model or with a decimal reaction order of 1.4, highlighting a complex process with such TC molecules which do not expose high-affinity end groups for the surface of apatite. The adsorption isotherm was perfectly fitted to the Sips (Langmuir-Freundlich) model, while other models failed to describe it, and the Sips exponent greater than unity (1.08) suggested a joint impact of surface heterogeneity and positive cooperativity between adsorbed molecules. Finally, preliminary insights on TC release from pelletized nanocrystalline apatite, in aqueous medium and neutral pH, were obtained using a recirculation cell, indicating a release profile mainly following a Higuchi-like diffusion-limited rate. This work is intended to shed more light on the interaction between polar molecules not exhibiting high-affinity end groups and biomimetic apatites and is a starting point in view of the elaboration of biomimetic apatite-based bone scaffolds functionalized with polar organic drugs for a local delivery. © 2015 American Chemical Society.

Shaijumon M.M.,CNRS Inter-university Material Research and Engineering | Shaijumon M.M.,Indian Institute of Science | Perre E.,CNRS Inter-university Material Research and Engineering | Daffos B.,CNRS Inter-university Material Research and Engineering | And 3 more authors.
Advanced Materials | Year: 2010

Microbatteries with large area capacity and no power limitation can be obtained by designing 3D structured batteries. 3D electrodes composed of 30 nm-thick films of LiCoO 2 coating free-standing columns of Al current collector were achieved. By comparison with a planar electrode presenting an equivalent nominal capacity, a 3D electrode exhibits improved capacity retention: 68% of the nominal capacity at 8C instead of 11%. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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