Bourja L.,University of Toulon |
Bourja L.,University Ibn Zohr |
Bakiz B.,University of Toulon |
Bakiz B.,University Ibn Zohr |
And 6 more authors.
Journal of Solid State Chemistry | Year: 2011
Polycrystalline samples of (1-x) CeO2-x/2 Bi2O 3 phases, where x is the atom fraction of bismuth have been synthesized by the precipitation process and after the thermal treatment at 600 °C, under air. Samples are first characterized by the X-ray diffraction and scanning electron microscopy. To determine the samples specific surface areas, Brunauer-Emmett-Teller (BET) analyses have been performed. In the composition range 0≤x≤0.20, a cubic solid solution with fluorite structure is obtained. For compositions x comprised between 0.30 and 0.90, two types of T′ (or β′) and T (or β) tetragonal phases, similar to the well-known β′ or β Bi2O3 metastable structural varieties, are observed. However, the crystal cell volumes of these β′ or β Bi2O3 phases increase with the composition x in bismuth: this might be due to the presence of defects or substitution by cerium atoms, in the tetragonal lattices. Using X-ray diffraction profile analyses, correlations between bismuth composition x and crystal sizes or lattice distortions have been established. The solidgas interactions between these polycrystalline materials and air-CH4 and air-CO flows have been studied as a function of temperature and composition x, using Fourier transform infrared (FTIR) analyses of the conversions of CH 4 and CO gases into the CO2 gas. The transformations of CH4 and CO molecules as a function of time and temperature are determined through the intensities of FTIR CO2 absorption bands. Using the specific surface areas determined from BET analyses, these FTIR intensities have been normalized and compared. For all bismuth compositions, a low catalytic reactivity is observed with air-CH4 gas flows, while, for the highest bismuth compositions, a high catalytic reactivity is observed with air-CO gas flows. © 2010 Elsevier Inc. All rights reserved.
Mosqueda H.A.,Laboratoire Of Genie Des Materiaux Et Procedes Associes |
Crosnier O.,Laboratoire Of Genie Des Materiaux Et Procedes Associes |
Athouel L.,Laboratoire Of Genie Des Materiaux Et Procedes Associes |
Dandeville Y.,Laboratoire Of Genie Des Materiaux Et Procedes Associes |
And 4 more authors.
Electrochimica Acta | Year: 2010
Different aqueous-based electrolytes have been tested in order to improve the electrochemical performance of hybrid (asymmetric) carbon/MnO2 electrochemical capacitor (EC). Chloride and bromide aqueous solutions lead to the formation of Cl2 and Br2 respectively upon oxidation of the corresponding salt, thus limiting the useful electrochemical window of the MnO2 electrode and producing gas evolution (in the case of chloride salts) detrimental to the cycling ability of an hybrid device. For sulfate and nitrate salts, MnO2 electrode exhibits a 20% increase in capacitance when lithium is used as the cation compared to sodium or potassium salts, probably due to partial lithium intercalation in the tunnels of α-MnO2 structure. The higher ionic conductivity and solubility of LiNO3 has led to the investigation of this electrolyte in carbon/MnO2 supercapacitor compared to standard hybrid cell using K2SO4. A lower resistance increase was evidenced when the temperature was decreased down to -10 °C. Long term cycling ability of carbon/MnO2 supercapacitor was also evidenced with 5 M LiNO 3 electrolyte. © 2010 Elsevier Ltd. All rights reserved.