Effect of CeO2 Presence on the Electronic Structure and the Activity for Ethanol Oxidation of Carbon Supported Pt

Pt/CeO2/C electrocatalysts in different compositions were prepared and their structural characteristics and activities for ethanol oxidation in alkaline media were evaluated. In the presence of CeO2, an increase in the platinum particle size was observed. XANES measurements indicated that the Pt d-band vacancies increased with increasing CeO2 amounts. For the first time, the decrease in electro activity was described to an electronic effect for high CeO2 contents. The dependence of the activity for ethanol oxidation on CeO2 content went to a maximum, due to the counteracting bifunctional and electronic effects of the metal oxide

Synthesis, Characterization and CO Tolerance Evaluation in PEMFCs of Pt2RuMo Electrocatalysts

Pt2RuMo/C catalysts were synthesized by the modified polyol method in the presence and absence of Li(C2H5)3BH (LBH), annealed at 600 °C under H2 atmosphere to improve the reduction of Pt and Ru to provide stronger interactions between Mo and another metals. LBH affected the physico-chemical characteristics of Pt2RuMo, that is, in the presence of LBH an increment of Mo(IV) amount and a decrease in the PtRu alloying degree were observed. The catalytic activity for hydrogen oxidation in the presence and absence of CO (CO tolerance) of the Pt2RuMo/C catalysts as anodes in polymer electrolyte membrane fuel cells (PEMFCs) was compared to that of a commercial PtRu/C catalyst. The results indicated that the CO tolerance increased with an increase in Mo(IV) content, but the stability increased with an increment of the amount of Ru oxides in the catalysts

Preparação e caracterização de eletrodos monocristalinos Preparation and characterization of single crystal electrodes

<abstract language="eng">Studies of the kinetics of electrocatalytic reactions on well oriented single crystal surfaces have demonstrated the influence of surface structure on the rate and mechanisms of many electrochemical processes. The preparation and characterization of these surfaces is the first step in this type of studies. In this paper, a methodology employed in order to ensure the quality and cleanliness of single crystals and their utilization as rotating electrodes is described

Metodologia para o crescimento de esferas monocristalinas de metais nobres A methodology for the growing of single crystal spheres of noble metals

<abstract language="eng">This paper describes in detail a technique employed to grow quasi-spherical single crystals of noble metals for electrochemical applications, using platinum as an example. The metal beads were formed by melting the extremity of a wire in an oxygen / butane flame. X-ray techniques were used to check the crystallization and to determine the orientation of the crystals. Treatment with a pure hydrogen flame followed by a cooling procedure in a hydrogen / argon atmosphere were used for conditioning the well-defined platinum single crystal surfaces. Finally, electrochemical characterization of the Pt(111), Pt(110) and Pt(100) surfaces was done in diluted sulfuric acid solution in the hydrogen adsorption / desorption potential region

Well-Alloyed PtFe/C Nanocatalysts of Controlled Composition and Same Particle Size: Oxygen Reduction and Methanol Tolerance

A study of the effect of iron concentration on the electrocatalysis of oxygen reduction reaction (ORR) on well-alloyed carbon-supported 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 bis(2-ethylhexyl)sulfosuccinate (AOT)+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 atoms), 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.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq