Emanuela Negro

Bicontinuous microemulsions for high yield wet synthesis of ultrafine platinum nanoparticles: effect of precursors and kinetics.

We demonstrate that for high yield wet synthesis of monodispersed nanoparticles high surfactant content bicontinuous microemulsions offer an advantageous template as particle size is limited by the embedding matrix whereas particle aggregation is largely prohibited by its structure. We synthesized platinum nanoparticles varying the reaction rate, metal precursor and reducing agent type and concentration, and the composition of the microemulsion in water content and oil type. High yields of up to 0.4% of metal produced per weight of template were achieved without affecting the particle size, ca. 2 nm. We showed that our method is robust in the sense that particle size is hardly dependent on synthesis conditions. This is attributed to the fact that the packing of surfactant on nanoparticle surfaces is the only parameter determining the particle size. It can only be slightly varied with ionic strength, headgroup hydration, and tail solvency through oil variation. Water content mainly affects the microemulsion stability and through that the colloidal stability of the nanoparticles. Hydrazine as a reducing agent poses a special case as it causes dimerization of the surfactant and hence modifies the surfactant parameter as well as the stability. Finally, we highlighted the differences in comparison to nanoparticle synthesis in standard water-in-oil microemulsions, and we propose a mechanism of particle formation.

Environmentally Friendly Carbon‐Preserving Recovery of Noble Metals From Supported Fuel Cell Catalysts

The dissolution of noble-metal catalysts under mild and carbon-preserving conditions offers the possibility of in situ regeneration of the catalyst nanoparticles in fuel cells or other applications. Here, we report on the complete dissolution of the fuel cell catalyst, platinum nanoparticles, under very mild conditions at room temperature in 0.1 M HClO4 and 0.1 M HCl by electrochemical potential cycling between 0.5-1.1 V at a scan rate of 50 mV s(-1) . Dissolution rates as high as 22.5 μg cm(-2) per cycle were achieved, which ensured a relatively short dissolution timescale of 3-5 h for a Pt loading of 0.35 mg cm(-2) on carbon. The influence of chloride ions and oxygen in the electrolyte on the dissolution was investigated, and a dissolution mechanism is proposed on the basis of the experimental observations and available literature results. During the dissolution process, the corrosion of the carbon support was minimal, as observed by X-ray photoelectron spectroscopy (XPS).