A phase diagram of the pseudo-ternary Aerosol OT (AOT)+n-butanol/n-heptane/water system, at a mass ratio of AOT/n-butanol=2, is presented. Conductivity measurements showed that within the vast one-phase microemulsion region observed, the structural transition from water-in-oil to oil-in-water microemulsion occurs continuously without phase separation. This pseudo-ternary system was applied to the synthesis of carbon-supported Pt70Fe30 nanoparticles, and it was found that nanoparticles prepared in microemulsions containing n-butanol have more Fe than those prepared in ternary microemulsions of AOT/n-heptane/water under similar conditions. It was verified that introducing n-butanol as a cosurfactant into the AOT/n-heptane/water system lead to complete reduction of the Fe ions that allowed obtaining alloyed PtFe nanoparticles with the desired composition, without the need of preparing functionalized surfactants and/or the use of inert atmosphere.

A study of the effect of iron concentration on the electrocatalysis of oxygen reduction reaction ͑ORR͒ on well-alloyed carbonsupported PtFe nanocatalysts with a controlled iron content and the same particle size is presented. To obtain the catalysts for this study, PtFe nanoparticles of different compositions were first obtained in a colloidal state in sodium bis͑2-ethylhexyl͒sulfosuccinate ͑AOT͒+n-butanol/n-heptane/water microemulsions and subsequently supported in high surface area carbon powder. Transmission electron microscopy evidenced that all PtFe/C nanocatalysts prepared are monodispersed and have nearly the same average particle size. X-ray diffraction studies showed that the lattice parameter of these PtFe/C catalysts varies linearly with iron content up to 50% ͑in atoms͒, while the compositions of the alloyed phases estimated by using Vegard's law are almost identical to the nominal values, indicating a high degree of alloying. The electrocatalytic activity for ORR of these catalysts was studied using the rotating disk electrode technique in O 2 saturated 0.5 mol L −1 H 2 SO 4 solutions, while methanol tolerance was evaluated from curves taken in acid solutions containing 0.1 mol L −1 methanol. The results reported here reflect the dependence of the electrocatalytic activity for the ORR on iron concentration in the absence of particle size effects and metal segregation. The growing awareness of the risks related to human-induced climate change has considerably raised the necessity of alternative ways of energy production. In this context, the conversion of chemical energy into electricity has become increasingly important and, thus, clean and efficient devices such as fuel cells are now attracting a great deal of attention from governments, academic institutions, and private businesses. While fuel cells might help to overcome the power problems, there are still a number of issues to be worked out to make the generation of electrical power using fuel cells practical and cost-effective.Among the different fuel cell types, the proton exchange membrane fuel cell ͑PEMFC͒ is considered the most adequate for vehicle and portable applications. However, much needs to be done to improve the performance. Among other problems, the slow kinetics of the oxygen reduction reaction ͑ORR͒ remains one of the key factors affecting the performance of PEMFCs, causing overpotential losses of ϳ0.3 to 0.4 V under typical operation conditions.

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Carbon-supported PtFe nanoparticles having similar overall composition (3:1), crystallinity, and average particle diameter were prepared with and without a Pt-skin layer and used to evaluate the extent, on the nanometer scale, of Pt-skin effects on the activity for oxygen reduction. In this study, we show that when most of the relevant properties of the catalysts are kept alike, there is an increase of about 2-fold in the intrinsic activity for oxygen reduction that can be ascribed to Pt-skin effects. It is also demonstrated that the activity improvement produced by the presence of a Pt-skin surface is, however, insufficient to generate significant differences on the power density of a single proton exchange membrane fuel cell.