Joelma Perez

The Electro-oxidation of Ethanol on Pt-Ru and Pt-Mo Particles Supported on High-Surface-Area Carbon

The oxidation of ethanol was studied on Pt-Ru and Pt-Mo electrocatalysts, supported on high-surface-area carbon, prepared by reduction with formic acid. The catalysts, containing up to 40 atom % of the second metal, were characterized by X-ray diffraction, energy-dispersive X-ray analyses and X-ray absorption experiments. The oxidation of ethanol was studied by cyclic voltammetry, chronoamperometry, and differential electrochemical mass spectroscopy experiments. Within the conditions used in this work, it was found that the activity for ethanol oxidation increased with the contents of the second metal and with the concentration of ethanol.

Structure sensitivity of oxygen reduction on platinum single crystal electrodes in acid solutions

Abstract The oxygen reduction reaction (orr) on the low index planes of single crystal Pt electrodes has been studied in HClO4 and H2SO4 solutions using the hanging meniscus rotating disk technique (HMRD). Significant structural sensitivity of the reaction rate has been found in both electrolytes. Results are compared with published data. The importance of controlling the conditions of the experiments, as well as the use of the correct hydrodynamic equations for the HMRD is also discussed.

Electrocatalytic oxidation of methanol: study with Pt:Mo dispersed catalysts

The electrocatalytic oxidation of methanol on Pt:Mo dispersed on carbon prepared using an alternative method recently developed in this laboratory was investigated. The EDX analysis confirmed that the simultaneous reduction of the precursor salts of Pt and Mo leads to the presence of these materials at the nominal composition initially calculated. The addition of Mo to Pt causes an increase of the oxidation currents, but does not improve the catalytic effect for methanol oxidation. Tafel plots for various methanol concentrations showed the presence of two slopes. On line differential electrochemical mass spectrometry (DEMS) was used to investigate the distribution of products and intermediates in methanol oxidation.

Impedance Studies of the Oxygen Reduction on Thin Porous Coating Rotating Platinum Electrodes

This paper presents a study of the oxygen reduction reaction on platinum on carbon thin porous coating rotating disk electrodes in 1.0 M NaOH and 0.5 M H 2 SO 4 solutions using ac impedance spectroscopy. The results are analyzed and simulated with the thin film/flooded agglomerate model. It is observed that the experimental system presents only one semicircle on Nyquist plots, because the processes in the agglomerate and the diffusion in the thin film are masked by the large value of the double layer capacitance. However, fitting of the impedance plots with the theoretical model leads to the conclusion that the processes in the agglomerate and in the thin film play important roles on the behavior of the electrode. The kinetic parameters obtained from the ac measurements are totally consistent with those observed in the dc experiments.

Effect of the degree of alloying of PtRu/C (1:1) catalysts on ethanol oxidation

The effect of alloying degree on the ethanol oxidation activity of a PtRu/C catalyst with a Pt/Ru atomic ratio of 1:1 was investigated by measurements in a half-cell and in a single direct ethanol fuel cell. The increase of the amount of Ru alloyed from one third to two thirds of the total Ru content in the catalyst clearly resulted in a decrease of the ethanol oxidation activity. As the amount of the highly active hydrous ruthenium oxide was near the same, the lower activity of the PtRu/C catalyst with higher alloying degree was mainly ascribed to the presence of an excessive number of Ru atoms around Pt active sites, hindering ethanol adsorption on Pt sites. The reduced ethanol adsorption could be also related to the decreased Pt–Pt bond distance and to the electronic effects by alloying.

Oxygen Reduction on PtFe/C Electrocatalysts Prepared in Microemulsions

Departamento de Fisico Quimica Institute de Quimica Universidade Estadual Paulista (UNESP), CP 355, Araraquara, SP 14801-970

Metodologia para o crescimento de esferas monocristalinas de metais nobres

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.

Anode Catalysts for Alkaline Direct Alcohol Fuel Cells and Characteristics of the Catalyst Layer

The faster kinetics of the alcohol oxidation reaction in alkaline direct alcohol fuel cells (ADAFCs), opening up the possibility of using less expensive metal catalysts, as silver, nickel, and palladium, makes the alkaline direct alcohol fuel cell a potentially low-cost technology compared to acid direct alcohol fuel cell technology, which employs platinum catalysts. In this work an overview of catalysts for ADAFCs, and of testing of ADAFCs, fuelled with methanol, ethanol, and ethylene glycol, formed by these materials, is presented.

Activity, mechanism, and short-term stability evaluation of PtSn-rare earth/C electrocatalysts for the ethanol oxidation reaction

Rare earths (RE) have been studied in the literature as additives in Pt and PtSn catalysts for the ethanol oxidation reaction (EOR), but their stability and influence on the mechanism of the EOR have not been reported. In this work, PtSnRE/C (RE: La, Ce, and Pr) catalysts were obtained by the polyol method, characterized, and their stability toward the EOR evaluated by cycling at two different potential ranges. The accelerated aging tests indicated that despite the changes in the CO stripping profiles, the ternary catalysts exhibit higher current densities after aging than Pt/C and PtSn/C catalysts. Even after dissolution of the rare-earth metals, as observed by energy-dispersive X-ray spectroscopy (EDS) before and after aging, the EOR activity after short-term stability tests was found to be higher than the initial one. The addition of these metals facilitates the retention of tin in the material, contributing to the overall stability of the bimetallic catalyst. The oxidation products of the ternary catalysts were evaluated by in situ Fourier transform infrared spectroscopy (FTIR) spectroscopy and high-performance liquid chromatography (HPLC), where the major products were found to be acetaldehyde and acetic acid, with only small concentrations of CO2. The improvement in the ethanol oxidation efficiency by PtSnRE/C catalysts can be explained by a bifunctional mechanism in which the rare-earth oxides are able to provide oxygenated species at low potentials.

9 EFFECT OF FLUSHING WITH PROTEIN SOURCES OF DIFFERENT DEGRADABILITY ON OVULATION NUMBER IN Santa Ines EWES

Flushing provides sheep a diet dense in nutrients before the breeding season to increase the ovulation rate and is usually accompanied by increase in body weight (BW) and body condition score (BCS). Although the effect of flushing with high-energy diets is documented, the influence of flushing with high-protein diets on ovulation rate and on plasma urea nitrogen (PUN) is not well established. The aim of this study was to evaluate the ovulation rate of Santa Ines ewes subjected to flushing with protein sources with different ruminal degradability. Forty-eight ewes were assigned to 2 treatments in a randomized block design, based on initial BCS (2.25 to 2.5; 2.75; and 3.0 to 3.25; scale 1 = thin and 5 = fat). The treatments consisted of 2 isonitrogenous (12% crude protein) and isocaloric (3.9 Mcal of metabolizable energy per day) diets, but with different proportions of rumen-degradable protein; one with soybean meal (SM, n = 24) and the other with corn gluten meal and cottonseed meal (CG + CM, n = 24), provided for 28 d before ovulation. The BW and BCS were evaluated weekly. Estrus synchronization was initiated on Day 17 after beginning the treatment diets. An intravaginal sponge with 60 mg of medroxyprogesterone acetate (MAP-60®, Tecnopec, Sao Paulo, Brazil) was used for 11 d, and an injection of 300 IU of eCG (Novormon®, Syntex SA, Buenos Aires, Argentina) and 50 μg of cloprostenol (Prolise®, ARSA S.R.L., Buenos Aires, Argentina) was given 9 d after beginning the protocol. Estrus was monitored twice daily. The ovulation rate was evaluated by transrectal ultrasonography and was characterized by the disappearance of dominant follicles in the ovaries. Blood samples for determination of PUN were collected on Days 7, 14, 21, and 28 after the start of flushing. Quantitative data were subjected to ANOVA and the rate of estrus detection was analyzed by chi-square test. Treatment differences were considered significant if P 0.05) between ewes feed SM or CG + CM, respectively. Flushing with protein sources with different ruminal degradability did not alter the ovulation rate or the ovulatory follicle diameter in Santa Ines ewes. Funded by FAPEMIG, CNPq, TECNOPEC.