Spark plasma sintered carbon electrodes for electrical double layer capacitor applications

The spark plasma sintering (SPS) is an emerging process for shaping any type of materials (metals, ceramic, polymers and their composites). The advantage of such a process is to prepare densified ceramic materials in a very short time, while keeping the materials internal porosity. In the present work, we have used the SPS technique to prepare activated carbon-based electrodes for Electrochemical Double Layer Capacitor applications (EDLC). Self-supported 600 and 300µm-thick electrodes were prepared and characterized using of Electrochemical Impedance Spectroscopy and galvanostatic cycling in a non-aqueous 1.5MNEt4BF4 in acetonitrile electrolyte. Electrochemical performance of these sintered electrodes were found to be in the same range – or even slightly better – than the conventional tape-casted activated carbon electrodes. Although organic liquid electrolyte was used to characterize the electrochemical performance of the sintered electrodes, these results demonstrate that the SPS technique could be worth of interest in the ultimate goal of designing solid-state supercapacitors

Nanocrystallized ceria-based coatings prepared by electrochemistry on TA6V titanium alloy

Nanocrystallized ceria-based coatings were prepared on TA6V titanium alloy by using a three-step procedure: substrate pretreatment, electrochemical impregnation and final heat treatment. UV–vis and Raman in situ spectroscopies performed at the substrate interface during the electrochemical impregnation, showed experimentally for the first time that the interfacial deposit is made up of cerium hydroxide, incorporating also water molecules and nitrate ions coming from the electrolyte. Thermogravimetric analysis indicated also that the composition of the coating after the impregnation is given by the global formula CeO23.4H2O, while XRD analysis revealed that ceria with cubic fluorite crystalline structure is finally produced. Different preparation conditions were studied in view to control the nanosize of the supported ceria crystallites. It appeared that the final heat treatment is the most efficient operational parameter for the tuning of the particle size, that it can be thus well controlled from 5 to 30 nm between 300 and 700 8C

MnO2-coated Ni nanorods: Enhanced high rate behavior in pseudo-capacitive supercapacitor

Ni nanorods prepared by electrochemical growth through an anodized aluminium oxide membrane were used as substrate for the electrodeposition of MnO2 either in potentiostatic mode or by a pulsed method. Electrochemical deposition parameters were chosen for an homogeneous deposit onto Ni nanorods. Resulting Ni supportedMnO2 electrodes were tested for electrochemical performances as nanostructured negative electrodes for supercapacitors. They exhibited initial capacitances up to 190 F/g and remarkable performances at high charge/discharge rates

Effect of electric field polarization and temperature on the effective permittivity and conductivity of porous anodic aluminium oxide membranes

Porous insulators offer new opportunities for the controlled guest–host synthesis of nanowires for future integrated circuits characterized by low propagation delay, crosstalk and power consumption. We propose a method to estimate the effect of the electric field polarization and temperature on the electrical properties of different types of synthesized porous anodic aluminium oxide membranes. It results that the effective permittivity along the pore axis is generally 20% higher than the one in the orthogonal direction. The type of solution and the voltage level applied during anodization are the main parameters affecting the AAO templates characteristics, i.e. their porosity and chemical content. The values of permittivity of the final material, are typically in the range 2.6–3.2 for large pore diameter membranes including phosphorus element and having a low water content, and in the range 3.5–4 for the ones with smaller pores, and showing sulphur element incorporation. Moreover, the dc conductivity of the different membranes appears to be correlated to the pore density

Outstanding room-temperature capacitance of biomass-derived microporous carbons in ionic liquid electrolyte

A remarkable capacitance of 180 F·g−1 (at 5 mV·s−1) in solvent-free room-temperature ionic liquid electrolyte, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, was achieved in symmetric supercapacitors using microporous carbons with a specific surface area of ca. 2000 m2·g−1 calculated from gas sorption by the 2D-NLDFT method. The efficient capacitive charge storage was ascribed to textural properties: unlike most activated carbons, high specific surface area was made accessible to the bulky ions of the ionic liquid electrolyte thanks to micropores (1–2 nm) enabled by fine-tuning chemical activation. From the industrial perspective, a high volumetric capacitance of ca. 80 F·cm−3 was reached in neat ionic liquid due to the absence of mesopores. The use of microporous carbons from biomass waste represents an important advantage for large-scale production of high energy density supercapacitors

On the Dynamics of Charging in Nanoporous Carbon-Based Supercapacitors

Supercapacitors are electricity storage systems with high power performances. Their short charge/discharge times are due to fast adsorption/desorption rates for the ions of the electrolyte on the electrode surface. Nanoporous carbon electrodes, which give larger capacitances than simpler geometries, might be expected to show poorer power performances because of the longer times taken by the ions to access the electrode interior. Experiments do not show such trends, however, and this remains to be explained at the molecular scale. Here we show that carbide-derived carbons exhibit heterogeneous and fast charging dynamics. We perform molecular dynamics simulations, with realistically modeled nanoporous electrodes and an ionic liquid electrolyte, in which the system, originally at equilibrium in the uncharged state, is suddenly perturbed by the application of an electric potential difference between the electrodes. The electrodes respond by charging progressively from the interface to the bulk as ions are exchanged between the nanopores and the electrolyte region. The simulation results are then injected into an equivalent circuit model, which allows us to calculate charging times for macroscopic-scale devices

Improved electro-grafting of nitropyrene onto onion-like carbon via in situ electrochemical reduction and polymerization: tailoring redox energy density of the supercapacitor positive electrode

Herein, we report a improved method for the physical grafting of 1-nitropyrene (Pyr-NO2) onto highly graphitized carbon onion. This is achieved through a lowering of the onset potential of the pyrene polymerization via in situ reduction of the NO2 group. The additional redox activity pertaining to the reduced NO2 enables exceeding the faradaic capacity which is associated with the p-doping of the grafted pyrene backbone, as observed for pyrene, 1-aminopyrene, and unreduced Pyr-NO2. Theoretical calculations demonstrate the charge transfer and binding enthalpy capabilities of Pyr-NO2, which are significantly higher than those of the other two species, and which allow for improved p-stacking on the carbon surface. Upon 20 wt % grafting of Pyr-NO2, the capacity of the electrode jumps from 20 mAh g-1 electrode to 38 mAh g-1 electrode, which corresponds to 110 mAh g-1 per mass of Pyr-NO2 and the average potential is increased by 200 mV. Very interestingly, this high performance is also coupled with outstanding retention with respect to both the initial capacity for more than 4000 cycles, as well as the power characteristics, demonstrating the considerable advantages of employing the present in situ grafting technique

Polypyrrole-Fe2O3 nanohybrid materials for electrochemical storage

We report on the synthesis and electrochemical characterization of nanohybrid polypyrrole (PPy) (PPy/Fe2O3) materials for electrochemical storage applications. We have shown that the incorporation of nanoparticles inside the PPy notably increases the charge storage capability in comparison to the “pure” conducting polymer. Incorporation of large anions, i.e., paratoluenesulfonate, allows a further improvement in the capacity. These charge storage modifications have been attributed to the morphology of the composite in which the particle sizes and the specific surface area are modified with the incorporation of nanoparticles. High capacity and stability have been obtained in PC/NEt4BF4 (at 20 mV/s), i.e., 47 mAh/g, with only a 3% charge loss after one thousand cyles. The kinetics of charge–discharge is also improved by the hybrid nanocomposite morphology modifications, which increase the rate of insertion–expulsion of counter anions in the bulk of the film. A room temperature ionic liquid such as imidazolium trifluoromethanesulfonimide seems to be a promising electrolyte because it further increases the capacity up to 53 mAh/g with a high stability during charge–discharge processes

Aspectos Importantes sobre la estructura institucional del país para la adopción de una gran estrategia marítima integrada en el Perú.

El presente trabajo intenta plantear aspectos importantes sobre la estructura institucional del país, para la adopción de una gran estrategia marítima integrada, resaltando la importancia de ésta en el desarrollo de los intereses marítimos del país. En primer lugar hacemos una reflexión respecto a la visión geoestratégica del Perú y revisamos la situación actual de los intereses marítimos peruanos. Luego evaluamos la estructura institucional del país y su contribución en la adopción de una estrategia marítima integrada. Posteriormente, se hace un análisis de las Políticas Marítimas adoptadas por Australia, Brasil, Canadá, Colombia, Portugal y la Unión Europea, empleando el método comparativo de políticas nacionales, para finalmente determinar algunos aspectos centrales sobre la estructura institucional y la gobernanza en el ámbito marítimo, que pueden ser aplicadas en el Perú

Aspectos Importantes sobre la estructura institucional del país para la adopción de una gran estrategia marítima integrada en el Perú.

El presente trabajo intenta plantear aspectos importantes sobre la estructura institucional del país, para la adopción de una gran estrategia marítima integrada, resaltando la importancia de ésta en el desarrollo de los intereses marítimos del país. En primer lugar hacemos una reflexión respecto a la visión geoestratégica del Perú y revisamos la situación actual de los intereses marítimos peruanos. Luego evaluamos la estructura institucional del país y su contribución en la adopción de una estrategia marítima integrada. Posteriormente, se hace un análisis de las Políticas Marítimas adoptadas por Australia, Brasil, Canadá, Colombia, Portugal y la Unión Europea, empleando el método comparativo de políticas nacionales, para finalmente determinar algunos aspectos centrales sobre la estructura institucional y la gobernanza en el ámbito marítimo, que pueden ser aplicadas en el Perú