Electrochemical reactivity and stability of platinum nanoparticles in imidazolium-based ionic liquids

"The original publication is available at www.springerlink.com"International audienceThe electrocatalytic activity of synthesized quasispherical Pt nanoparticles (NPs) has been studied, taking as amodel the COads electrooxidation reaction in two imidazolium-based ionic liquids such as 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4mim+][NTf2−] and 1-butyl-3-methylimidazolium tetrafluoroborate [C4mim+][BF4−]. In particular, the effect of (i) watercontent, (ii) temperature, and (iii) nature of the roomtemperature ionic liquid (RTIL) on the electrocatalytic behavior of these Pt NPs has been systematically evaluated. The obtained results show how important are those parameters, since the COads oxidation peak potential exhibits a great sensitivity depending on the water content, temperature, and nature of the RTIL used. Interestingly, the charge density associated with the COads electrooxidation peak strongly dependson the nature of the ionic liquid, which reflects the complexity of this electrocatalytic reaction in this media. Moreover, Pt NP electrocatalyst degradation in those RTILs, considered as a loss of electrochemically active area, has been evaluated and shows high stability despite the extreme potentials afforded in RTILs

Chemical limits on X-ray nanobeam studies in water

Operando X-ray studies of chemical reactions have gained increasing interest lately, fuelled by the emergence of a new generation of powerful focused X-ray sources. Although it is well known that ionizing radiation causes damage to samples via radical chemistry, this effect is often overlooked in studies of working devices or catalysts where intense focused beams are used as nano-scale probes. Here, we show how an X-ray nano-beam directly causes a phase transition in Pd nanoparticles, and that a large oxidative potential must be applied to prevent the process. We present a chemical reaction-diffusion model which offers a plausible qualitative explanation of the observations, and which also suggests that prohibitive concentrations of reactive species will arise under any focused X-ray probe, calling into question the validity of these methods as applied to aqueous chemical and catalytic systems

Rapid screening of silver nanoparticles for the catalytic degradation of chlorinated pollutants in water

International audienceElectrochemical abatement of volatile polychlorinated organic compounds for environmental applica-tions represents a very attractive and feasible alternative for working at mild reaction conditions andreduced costs. We present herein the synthesis of three different sized Ag nanoparticles (NPs) and theirelectrocatalytic performance in the degradation of a model pollutant (trichloromethane, CHCl3) in aque-ous media. Two different methodologies are used: A conventional study based on voltammetry andchronoamperometry and a novel screening approach based on the micropipette delivery/substrate col-lection (MD/SC) mode of the scanning electrochemical microscopy (SECM). This new approach allows todose any reactant, in this case CHCl3, even if the latter cannot be electrogenerated. Moreover, we intro-duce here a novel platform for studying nanomaterials by reducing the current collector backgroundcontribution using disposable screen-printed array electrodes. The performance ranking obtained bythe SECM for the three different samples of Ag NPs synthesized is validated by its comparison with theresults obtained by chronoamperometry, which demonstrates the feasibility and the good sensitivity ofSECM in electrocatalysts screening for the CHCl3reduction reaction. In addition, SECM allows to analyzesimultaneously a large number of catalysts in one single experiment under constant experimental con-ditions. We suggest the proper size range and the presence of abundant superficial defective sites, suchas steps or kinks, as the main reasons for Ag NPs C1 exhibiting the best overall catalytic performance intrichloromethane electrochemical reduction