Synthesis of Highly Porous Catalytic Layers for Polymer Electrolyte Fuel Cell Based on Carbon Aerogels

International audienceRecent studies of the PEMFC catalytic layer electrocatalystsupport showed that high surface area carbon blacks cannot beused efficiently (1) because they have necessarily small primarypores that yield high diffusion limitation for the oxygenreduction reaction (ORR). In the present paper, we firstsynthesized and characterized carbon aerogels which exhibit highsurface area, high porous volume and adjustable pore-sizedistribution. In that way, they enable to decouple betweensurface area and porosity, while they are also promisingelectrocatalyst supports (2). Second, we elaborated newcatalytic layers made from 2 different carbon aerogels with 2different Nafion loadings. Finally, we characterized thestructure of such catalytic layers, and evaluated their activitytowards the oxygen reduction reaction (ORR). Finally, anappropriate catalyst support should display large pore-size andhigh surface area in order to reduce the PEMFC cathode platinumloadings without loosing activity, following the reduction ofoxygen diffusion limitation

ELECTROMICROGRAVIMETRIC STUDY OF THALLIUM UNDER POTENTIAL DEPOSITS ON GOLD IN ACID MEDIUM

International audienceA study of underpotential deposits (UPD) of Tl/Au was carried out by coupling microgravimetry to cyclic voltammetry in acid perchlorate medium. In the first place, it was found that in the potential region positive to UPD formation of thallium on gold, the recorded frequency did not vary, thus implying that the adsorption of perchlorate anions does not take place before the formation of a metallic monolayer. In the second place, adsorption isotherms prepared from these systems presented similar forms to those appearing when using single-crystal electrodes of Au(111) from the literature. Besides, our results showed that the adsorption of this metal on gold substrates involves species that completely transfer their charge in accordance with the models existing in the literature. Studies performed during the time passed at the cathodic limit of the voltammogram show that there is no formation of any alloyed phase or of 2D phases in the underpotential region. Finally, a monolayer-equivalent charge was determined to be higher than the theoretical, which seems to show that, on the microscopic level, the roughness has a determinant role in the interpretation of these result

Electromicrogravimmetric Study of the Effect of Cl Anions on Thallium Underpotential Deposition Onto Gold

International audienceThe effect of chloride adsorption on underpotential deposition of thallium onto gold electrode was studied using cyclic voltammetry coupled with microgravimetry. The results obtained suggest the existence of two potential regions with different processes occurring during Tl UPD in the presence of anions. In the first zone, at low coverage, there are two simultaneously occurring processes: desorption of all chloride atoms, which are adsorbed on the gold substrate prior to the onset of Tl UPD, and thallium adsorption on the energetically most favorable sites (grain boundaries, steps, etc) present on the electrode surface. During these processes a strong interaction among thallium atoms is induced by the presence of chloride atoms on the adjacent sites. This strong interaction generates sharper current peaks in the voltammogram, associated with the above processes, and their displacement towards cathodic potentials proportional to the anion concentration. However, in the second potential zone at high coverage, the adsorption of thallium atoms takes place on the least accessible sites (terraces) on the gold substrate. In this type of sites, the effect of the presence of chloride atoms on the UPD process is unimportant

Chemical Evolution of SiC Particles Surface in Salt Solution

International audienceWATT bath solution is constituted of NiCl2, NiSO4 with a pH value fixed to 3 with H3BO4. This solution is used as electrolyte for SiC co deposition from Ni/SiC system. The very good embedment of the particles noticed with this solution is due to particles` surface state at this pH value. Particles` surfaces are constituted of chemical groups which, interacting with solutions, play a rule in the surface state. The experimentations undertaken pulled out that the interaction between the electrolyte and groups such as SiO3C and SiC2O2 for example present at the particles` surface, governs zeta potential, which control SiC particles embedment in the nickel matrix. At pH 3 particles are neutral by adsorbing positive and negative species. When they are transported to the reduction pole, the negative adsorbed species are vanished; the particles become positively charged by the silanol protonated groups. As the kinetic of proton reduction is slower then nickel ions one at pH 3, the particles are stuck at the cathode surface and embedded in nickel electrodeposited matrix

Electromicrogravimmetric Study of the Effect of Cl Anions on Thallium Underpotential Deposition Onto Gold

International audienceThe effect of chloride adsorption on underpotential deposition of thallium onto gold electrode was studied using cyclic voltammetry coupled with microgravimetry. The results obtained suggest the existence of two potential regions with different processes occurring during Tl UPD in the presence of anions. In the first zone, at low coverage, there are two simultaneously occurring processes: desorption of all chloride atoms, which are adsorbed on the gold substrate prior to the onset of Tl UPD, and thallium adsorption on the energetically most favorable sites (grain boundaries, steps, etc) present on the electrode surface. During these processes a strong interaction among thallium atoms is induced by the presence of chloride atoms on the adjacent sites. This strong interaction generates sharper current peaks in the voltammogram, associated with the above processes, and their displacement towards cathodic potentials proportional to the anion concentration. However, in the second potential zone at high coverage, the adsorption of thallium atoms takes place on the least accessible sites (terraces) on the gold substrate. In this type of sites, the effect of the presence of chloride atoms on the UPD process is unimportant

Extraction of iridium( iv ) from aqueous solutions using hydrophilic/hydrophobic ionic liquids

International audienceAnionic complexes of iridium(IV) were extracted from acidic solutions of HCl using ionic liquids (IL). The influence of the cationic structure of IL and of the aqueous phase pH on the distribution coefficients of IrCl62− was investigated. Liquid–-liquid extraction and precipitation of iridium(IV) were studied. Iridium(IV) was precipitated from aqueous solutions using water-soluble ionic liquids by forming a water-insoluble salt composed of two cations from the ionic liquid. Pyridinium cations appear to be the most efficient at precipitating iridium(IV). Iridium(IV) was found to be efficiently extracted using simple hydrophobic ionic liquids, exhibiting D values ranging up to 71. Investigations on the extraction mechanism tend to show that iridium(IV) is exchanged with two [NTf2]− anions from the IL phase. Finally, elution of iridium(IV) from ionic liquids towards aqueous solutions was carried out from [BMIM][NTf2], [OMIM][NTf2] or [OdMIM][NTf2] into solutions containing high amounts of hydrochloric acid or nitric acid

Method of oxidation in a molten salt bath

The invention relates to a method for upgrading waste comprising org. components in a bath of molten salt(s)​, comprising the following steps: supplying (1) to a reactor, at least one salt or a mixt. of salts comprising at least one alkali metal hydroxide; supplying (2) the waste to the reactor; heating (3) the reactor at a temp. above the m.p. of the salt. Thus, the salt supplied melts to form a liq. reaction medium, and induce an at least partial oxidn. (4) of the org. components. At least one compd. resulting from this oxidn. (4) is recovered (5)​. At least one alkali metal hydroxide comprises water of crystn., acting as oxidizing agent for the org. components in the reaction medium, so as to participate in a prodn. of dihydrogen, the latter being recovered (52) for the upgrading thereof

Anodic behavior of gold in 1-butyl-3-methylimidazolium methanesulfonate ionic liquid with chloride anion

International audienceThe anodic behavior of gold has been investigated in presence of chloride and/or water in 1-butyl-3-methylimidazolium methanesulfonate (BMI CH3SO3) ionic liquid (IL). The cyclic voltammetry (CVs) in presence of chloride ions shows two waves attributed to the oxidation of the gold electrode which occurs under two steps: the first one is attributed to the electrochemical dissolution of gold into to gold(I), while the second one is attributed to an overlap of the chloride oxidation step as well as the oxidation of Au(I) to Au(III). Furthermore the determination of water and chloride content in IL allowed observing that the passive layer induced by water could be removed under chloride. Thanks to those results we were able to clarify the conditions of gold recovering in this kind of electrolyte