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Souad Mokrane Laïd Makhloufi Nicolas Alonso-Vante 《Journal of Solid State Electrochemistry》2008,12(5):569-574
Conducting polypyrrole (PPy)/C (Vulcan XC-72) composite materials were synthesized by chemical polymerization method. These
materials were used as matrix to support platinum nanoparticles, which were produced by the carbonyl chemical route. For the
same catalyst loading (50 μg cm−2), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum
toward the oxygen reduction reaction in acid medium. The variation of the PPy/C ratio determines the so-called substrate effect
for electrocatalysis.
Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to
interfacial electrochemistry. 相似文献
2.
Abdel-Ghani Boudjahem Tahar Mokrane Affef Redjel Mohammed M. Bettahar 《Comptes Rendus Chimie》2010,13(12):1433-1439
Palladium catalysts (1–10 wt.% Pd) supported on silica were prepared by hydrazine reduction of palladium chloride at room temperature. They were characterized by XRD, TEM, EDX, H2-adsorption, and H2-TPD and tested in the gas phase hydrogenation of benzene in the temperature range 75–250 °C. A conventional catalyst (1 wt.% Pd) obtained by calcination then hydrogen reduction of the same metal precursor was studied for comparison. Metal particles with a size range 6.8–28.4 nm were obtained. Dispersion, hydrogen storage and activity in benzene hydrogenation increased with decreasing particle size. In comparison, the classical catalyst was found much more dispersed (mean particle size of 1.6 nm) and more active (specific rate 1.6–3.7 times higher) than the homolog hydrazine catalyst. However, unexpectedly, turnover frequency (TOF) calculations indicated a greater reactivity of the metal surface atoms for the hydrazine catalyst. It also stored more hydrogen. These contrasting results are discussed in relation with the metal particle morphology. 相似文献
3.
Accolla M Congiu E Dulieu F Manicò G Chaabouni H Matar E Mokrane H Lemaire JL Pirronello V 《Physical chemistry chemical physics : PCCP》2011,13(17):8037-8045
The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H(2) formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H(2) is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the thickness of the ice and has a value of ?(0) = 2 × 10(16) D-atoms cm(-2) per layer of H(2)O. We also use a model which confirms that the binding sites on the porous ice are destroyed regardless of their energy depth, and that the reduction of the porosity corresponds in fact to a reduction of the effective area. This reduction appears to be compatible with the fraction of D(2) formation energy transferred to the porous ice network. Under interstellar conditions, this effect is likely to be efficient and, together with other compaction processes, provides a good argument to believe that interstellar ice is amorphous and non-porous. 相似文献
4.
S. Mokrane L. Makhloufi H. Hammache B. Saidani 《Journal of Solid State Electrochemistry》2001,5(5):339-347
Conductive polypyrrole (PPy) films and PPy films containing Ge microparticles were synthesized by anodic oxidation of pyrrole
in acidic nitrate solutions using a bare passivated titanium electrode. Well-adhering black PPy films were obtained both under
galvanostatic and potentiodynamic polarization. After the formation of the PPy film, during the first anodic cycle, an increase
of the anodic deposition current with the number of cycles was observed, revealing the increase of conductivity of the growing
film. The variations of the electrode surface area were estimated by impedance spectroscopy measurements. The kinetics of
the PPy film formation is controlled by diffusion of the Py monomer in the solution. The diffusion coefficient, estimated
by two different methods, was ca. 2×10–6 cm2 s–1. The reduction rate of oxygen and protons at the Ti/PPy/Ge electrodes depends on how the Ge microparticles are incorporated
in the PPy film. Optimum conditions for this incorporation are realized with thin PPy films and high Ge loading. Thermogravimetric
analysis shows that the PPy film containing Ge microparticles is more thermally stable than the blank PPy film.
Electronic Publication 相似文献
5.
Chehrouri M Fillion JH Chaabouni H Mokrane H Congiu E Dulieu F Matar E Michaut X Lemaire JL 《Physical chemistry chemical physics : PCCP》2011,13(6):2172-2178
Nuclear spin conversion (NSC) of ortho- to para-H(2) and para- to ortho-D(2) has been investigated on an amorphous solid water (ASW) surface at 10 K, in the presence of co-adsorbed O(2). The dynamics of the nuclear spin conversion could be revealed by combination of resonance enhanced multiphoton ionization spectroscopy (REMPI) with temperature programmed desorption (TPD) experiments. The conversion rates are consistent with a diffusion of molecular hydrogen inducing a nuclear spin conversion enhanced in the vicinity of molecular oxygen. The conversion times were found to increase with decreasing O(2) and H(2) coverage. Finally, on oxygen free ASW surface, the extremely long conversion characteristic times measured showed that such surface is not an efficient catalyst for NSC, in contradiction with hypothesis commonly made for interstellar medium. 相似文献
6.
Selective laser sintering (SLS) of polymer powders involves multiphysical transient phenomena. A numerical tool for simulating such a process is developed on the basis of the reliable modeling of the corresponding thermo-physical transient phenomena and appropriate numerical methods. The present paper addresses modeling, simulation, and validation aspects that are indispensable for studying and optimizing SLS process. The coupled multiphysical models are detailed, and the numerical tool based on the finite volume method is presented, with validations in terms of numerical and physical accuracy, by considering the shrinkage involved in the process and the successive layers deposition. A parametric analysis is finally proposed in order to test the reliability of the model in terms of representing real physical phenomena and thermal history experienced by the material during the process. 相似文献
7.
Mediterranean Journal of Mathematics - In this study, we consider Sturm–Liouville equation having a symmetric potential function under the separated boundary conditions on a finite interval.... 相似文献
8.
In this paper we prove the Lewy–Stampacchia's inequality for elliptic variational inequalities with obstacle involving fairly general Leray–Lions operators. The main novelty of the paper is the method of proof, which uses the natural penalization. One of the steps of the proof consists in proving, again thanks to the natural penalization, that the nonnegative cone of W
0
1,p
() is dense in the nonnegative cone of W-1,p(). 相似文献
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