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Porous activated carbon (AC) was successfully elaborated from olive stones and valued as an electrode material for electrical double-layer supercapacitors. The activated carbon surface was subsequently coated by silica to improve its physico-chemical and electrochemical properties. The treated activated carbon surface (AC-Si) exhibited a meso-microporous nature. From electrochemical investigations, an improvement of the capacitive behavior was demonstrated after the silica coating. When the bare activated carbon is used as electrode materials, the specific capacitance delivered by the assembled symmetric supercapacitor is 11 F g−1 at a current density of 0.5 A g−1 for an operating voltage of 0.6 V. However, the supercapacitor based on carbon–silica electrodes showed an obvious enhancement of the specific capacitance up to 141 F g−1 at 0.5 A g−1 and operated over a larger cell voltage of 1.25 V. For the AC-Si//AC-Si device, the exhibited specific energy is 30.6 Wh kg−1 and the specific power is 1661 W kg−1 at a current density of 0.5 A g−1. Therefore, the activated carbon derived from olive stones and coated by silica is a promising electrode material for supercapacitor devices.

The evaluation of the migration of metallic elements in the metal containers is usually performed through the direct analysis of the cans’ content. However, this may be biased by exogenous factors ...

Co3O4 powders are synthesized by a controllable microwave process in the presence of nonionic surfactants characterized by various structures. The influence of the surfactant structure on the charge storage performance of Co3O4 –based electrode is commented through the specific surface area and morphology of Co3O4 powder. In the absence of surfactants, Co3O4 layers are self-organized into microspheres. When linear PEG 2000 or Triton X100 polymers are used as surfactants, Co3O4 microspheres unfold into particles. However, a nanorods-like morphology is obtained with the multi-branched Tween 20 surfactant. Such a unique architecture exhibits remarkable electrochemical performance with high capacity and suitable cycle life after 2000 cycles in 3 M KOH aqueous solution. Increasing the specific surface area results in the improvement of the electrochemical performance. The specific capacity values deduced from cyclic voltammetry experiments are found to increase in the following order: Co3O4 -without surfactant (60 mAh g−1)

Mesoporous Co3O4 nanowires were uniformly deposited onto Ni foam by using a facile hydrothermal route. The as-prepared Co3O4@Ni materials were applied as electrodes for symmetric supercapacitors. The electrochemical performances of Co3O4@Ni were investigated in the presence of aprotic ionic liquids (ILs) and compared to KOH electrolyte. The selected ILs are composed by the same bis(trifluoromethylsulfonyl)imide (TFSI−) anion, paired with 1-Allyl-3-methylimidazolium (AMIM+) or 1-Ethyl-3-methylimidazolium (EMIM+) cations. The electrolytes composed by KOH and ILs were prepared in a polymer gel form. Independently on the electrolyte nature, the profiles of cyclic voltammograms and galvanostatic charge/discharge curves are indicative of an electrochemical double-layer charge storage mechanism. Combining our Co3O4@Ni electrodes with selected ILs polymer gel electrolytes showed good electrochemical stabilities with 85% and 97% retentions of the initial capacitances after 10,000 cycles in [AMIM-TFSI] and [EMIM-TFSI], respectively. At a current rate of 0.2 A g−1, the lowest values of specific energy (2.8 Wh kg−1) and specific power (201.9 W kg−1) were exhibited in the presence of KOH based gel electrolyte. This poor electrochemical performance was considerably improved by using aprotic ILs. For [AMIM-TFSI] and [EMIM-TFSI] based polymer gel electrolytes, high specific powers up to 811 and 680 W kg−1 were delivered at 0.2 A g−1 with enhanced specific energies of 29.4 and 23.3 Wh kg−1, respectively. Hence, the specific energies of the devices assembled by PVDF-HFP/AMIM-TFSI or PVDF-HFP/EMIM-TFSI polymer gel electrolytes were 8 to 10 times higher than that of the device assembled by PVA/KOH gel electrolyte.

The electrodeposition of silver was performed on a platinum electrode from a non-fluorinated ionic liquid (IL), butylpyridinium dicyanamide (Pyri4-DCA). The as-studied IL is characterized by a high ionic conductivity (11.03 mS.cm−1) and a low dynamic viscosity (24.4 mPa.s), which are appropriate for the electrodeposition process. The cyclic voltammetry (CV) curves recorded in Ag-DCA/Pyri4-DCA solutions showed the presence of reduction and oxidation peaks, respectively associated with the deposition and stripping of silver from the Pt surface. The diffusion coefficient of Ag(I) calculated from CV curves varied from 5.3 10−7 to 1.1 10−7 when Ag+ concentration was changed from 1 to 10 mM. The silver was electrodeposited on the Pt surface at different constant potentials. The nuclei size and population density of silver were monitored by varying the electrolyte concentration, the applied potential and the deposition time. From the analysis of the experimental transient curves, it was shown that the electrochemical deposition process of silver follows a 3D nucleation with diffusion-controlled growth. The nuclei population densities and diffusion coefficients were also determined for various chronoamperometric parameters by using the fitting model of Scharifker and Hills for 3D nucleation and growth.

Mg2Ni-based compounds were prepared using a high-energy milling technique, with a planetary ball mill, and subsequent annealing at 350 °C. X-ray diffraction analyses revealed that Mg2Ni phase was obtained after 10 milling hours, in addition to Ni phase. Increasing the ball-milling duration from 10 to 17 h causes a decrease in the crystal size of particles from 93 to 76 nm. However, the subsequent annealing of all Mg2Ni-based materials highly increases their crystallite sizes with calculated values in the range of 261–235 nm. In the same way, X-ray diffraction patterns of annealed compounds show the presence of highly crystallized Mg2Ni phases. The particle size of Mg2Ni/Ni particles is estimated at 25 µm after 10 milling hours and drops to 5 µm at longer times. The scanning electron microscopy images of Mg2Ni/Ni particles demonstrated a drastic increase of their sizes up to 100 µm upon annealing. The hydrogenation reactivity and kinetic of Mg2Ni/Ni were both characterized by solid–gas reactions. The hydrogen absorption capacity value was about 3.5 H/f.u for milled and annealed Mg2Ni/Ni compound. The highest hydrogen absorption kinetic was obtained during the first 5 h of absorption time, where 95 % of the maximum absorption capacity was reached.

International audience; A series of novel ionic liquids (ILs) based on N-allyl-N,N-dimethylethylammonium (N112A+) are synthesized and characterized. Their physical properties and electrochemical stabilities are investigated and discussed toward the anion constituents. Herein, four anions are studied including one planar non-fluorinated anion (DCA−) and three fluorinated anions (TFSI−, OTf−, TFA−). The experimental properties are compared to those predicted by density functional theory (DFT) calculations. All salts are found to be low melting compounds while being liquid at room temperature. N112A-TFSI is the most thermally stable (Td = 329 °C) and N112A-TFA is the least stable (Td = 158 °C). The temperature effect on ILs transport properties is determined and discussed using the ionicity and Angell's fragility concepts. Among the good and fragile prepared ILs, N112A –DCA exhibits outstanding transport properties thanks to the low dynamic viscosity (19.97 mPa·s) and high ionic conductivity (19.20 mS·cm−1) reached at 298 K. These suitable properties are explained, from theoretical calculations, by the lower intermolecular interactions of ion-pairs in N112A –DCA and quantified by the decreased value of dispersion ion-pairs interaction energy (−6 kJ·mol−1). The electrochemical stability window (ESW) of selected ILs is strongly affected by the anion structure. The ESW values are found to decrease in the following order N112A-TFSI (4.40 V) > N112A-OTf (3.80 V) > N112A-DCA (3.00 V) > N112A-TFA (2.18 V). Taking into account the most likely oxidation and reduction reactions, the ESWs are discussed and validated by the density-based solvent model (SMD). The experimental values of ESWs are very close to the predicted ones.