Role of oxygen-containing species at Pt(111) on the oxygen reduction reaction in acid media

The oxygen reduction reaction (ORR) is one of the fundamental reactions in electrochemistry and has been widely studied, but the mechanistic details of ORR still remain elusive. In this work, the role of electrochemically oxygenated species, such as adsorbed hydroxide, OHads, adsorbed oxygen, Oads, and Pt(111) oxide, PtO, in the ORR dynamics is studied by employing electrochemical techniques, i.e., combining rotating disk mass-transport control with potential sweep rate perturbation. In this framework, a reduction peak at 0.85 V, E ORR, is detected. This peak shows a different electrochemical dynamics than that of Pt(111) oxides. The data analysis suggests that neither OHads nor Oads are the main bottleneck in the mechanism. Instead, results support the reduction of a soluble intermediate species as the rate determining step in the mechanism. On the other hand, PtO species, which are generated at relatively high potentials and are responsible of surface disordering, strongly inhibit the ORR as long as they are adsorbed in the electrode surface.This study has been carried out in the framework of the European Commission FP7 Initial Training Network “ELCAT,” Grant Agreement No. 214936–2. Supports from the Spanish MINECO though project CTQ2013–44083-P and GV through PROMETEOII/2014/013 (FEDER) are greatly acknowledged

Oxygen reduction on nanostructured platinum surfaces in acidic media: Promoting effect of surface steps and ideal response of Pt(1 1 1)

In this paper, the role of surface steps on the electrocatalytic activity of platinum nanostructured surfaces for the oxygen reduction reaction (ORR) in acidic medium is evaluated by using stepped surfaces of structure Pt(S)[n(1 1 1) × (1 1 1)] with large terraces (20 ≤ n ≤ 50). It is realized that the inclusion of an even low amount of surface steps enhances the ORR, and linear activity trends are measured when currents at constant potential are plotted vs. the step density. As a consequence, an ideal ORR curve for a defect-free Pt(1 1 1) surface is extrapolated at zero defect density from experimental data and can be compared to that of a quasi-perfect Pt(1 1 1) electrode. It is clearly shown that surface steps promote the electrode activity toward ORR in acid medium. Results are discussed in light of available theoretical and experimental data.This work has been financially supported by a grant from COLCIENCIAS and the Universidad Nacional de Colombia in the framework of the National Program of Formation in Innovation Leaders (Contract No. 472 of 2007). Support from the Spanish MICYNN though project CTQ2010-16271 and GV through PROM-ETEO/2009/045 (FEDER) are also greatly acknowledged

Thermodynamic properties of hydrogen–water adsorption at terraces and steps of Pt(111) vicinal surface electrodes

In this work, the effect of temperature on the adsorption states of Pt(111) vicinal surface electrodes in perchloric acid is studied through a thermodynamic analysis. The method allows calculating thermodynamic properties of the interface. In this framework, the concept of the generalized isothermand the statistical thermodynamics description are applied to calculate formal entropies, enthalpies and Gibbs energies,ΔGi0, of the adsorption processes at two-dimensional terraces and one-dimensional steps. These values are compared with data from literature. Additionally, the effect of the step density onΔGi0 and on the lateral interactions between adsorbed species,ωij, at terraces and steps is also determined. Calculated ΔGi0 , entropies and enthalpies are almost temperature-independent, especially at steps, but they depend on the step orientation. In contrast,ΔGi0 and ωij at terraces depend on the step density, following a linear tendency for terrace lengths larger than 5 atoms. However, while ΔGi0 increases with the step density, ωij decreases. Results were explained by considering the modification in the energetic surface balance by hydrogen, Hads, andwater,H2Oads, co-adsorption on the electrode, which in turn determines the whole adsorption processes on terraces and steps.This study has been carried out in the framework of the European Commission FP7 Initial Training Network “ELCAT”, Grant Agreement No. 214936-2. Support from the Spanish MINECO though project CTQ2013-44083-P and GV through PROMETEOII/2014/013 (FEDER) are greatly acknowledged

Oxygen reduction at platinum electrodes: The interplay between surface and surroundings properties

In this work, recent progress in the understanding of the mechanism of the oxygen reduction reaction at Pt surfaces is shortly reviewed. Specifically, the presence of a soluble and short-lived intermediate different to H2O2 in the ORR reaction path and the interrelated effect between the surface arrangement, adsorption of oxygen-containing species and water structure in the ORR reactivity in acid environments are discussed. Besides, the influence of the proton concentration on the ORR product distribution, the existence of a chemical step and the possible role of the soluble intermediate as a bifurcation point in the mechanism are also analyzed.The authors would like to thank Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP - Procs. 2013/16930-7 and 2014/23486-9), Brazil (A.M.G-M) and the Spanish MINECO though project CTQ2016-76221-P (FEDER) and GV through PROMETEOII/2014/013 ( FEDER) (J.M.F.), for financial supports

Project - Based instruction for the appropriation of the strategic framework in 5 non-certified municipalities of Risaralda

Este proyecto de clase tuvo como propósito que tanto estudiantes bachilleres como docentes y directivos del Instituto Agropecuario Veracruz ubicado en Santa Rosa de Cabal y la Institución Educativa Instituto Guática; se apropien del Plan Educativo Institucional (PEI) mientras desarrollan sus habilidades en el idioma Inglés a través del trabajo colaborativo con el fin de lograr la visión 2032 Colombia bilingüe. Este proyecto se desarrolla a través de la metodología: Pedagogía Basada en Proyectos (Project-Based Instruction) el cual el estudiante es protagonista de su propio desarrollo académico a través de unas fases implementadas para su uso correcto. Debido a que no hubo una implementación directa del plan de clase por parte de las diseñadoras, se utilizaron diferentes métodos para la recolección de datos, estos fueron: entrevistas, formatos de reflexión y grabaciones de audio. Los resultados obtenidos al final de este proyecto fueron la incrementación de la motivación y participación de los estudiantes a través del trabajo colaborativo; además de la apropiación del PEI a través del proyecto el cual les permitió practicar las habilidades del Inglés en diferentes contextos

Electrocatalytic oxidation and reduction of H2O2 on Au single crystals

In this work, the reduction and oxidation of hydrogen peroxide on Au single crystals is studied in weakly adsorbing electrolytes. Results are discussed in terms of the potential of zero charge and the adsorption strength of different anions, which in turn depend on the crystallographic orientation of the electrode. Close to the reaction onset, both reactions follow the same activity trend with Au(100) and Au(111) being the most and the least active surface planes, respectively. At high potentials, gold oxides inhibit the oxidation of H2O2, which seems to be controlled by a surface process.Support from the Spanish MINECO though project CTQ2016-76221-P (FEDER) and GV through PROMETEOII/2014/013 (FEDER) are greatly acknowledged

Vitamina e y aceites vegetales

<font face="Helvetica" size="1"><p align="left">An interest in vitamin E has increased in recent years due to its potent antioxidant properties and its role in preventing age-related diseases, cardiovascular diseases or Alzheimer. This work describes the biogenesis, bioavailability, nutritional requirements, activity and properties of vitamin E. Vegetable oils constitute one of the main sources of vitamin E dietary intake and an extensive bibliographic revision of this vitamin in vegetable oils is carried out from four points of view: antioxidant properties, health benefits, effects of external agents and effects of processing on vitamin E content and analytical techniques used for its analysis.</p></font><br><br><font face="Helvetica" size="1"><p align="left">El inter&eacute;s por la vitamina E ha aumentado en los &uacute;ltimos a&ntilde;os debido a su potente poder antioxidante y a su papel frente a enfermedades relacionadas con la edad, trastornos cardiovasculares o Alzheimer. En este trabajo se detallan la biog&eacute;nesis, biodisponibilidad, requerimientos nutricionales, actividad y propiedades de la vitamina E. Los aceites vegetales constituyen una de las fuentes principales de aporte de vitamina E a trav&eacute;s de la dieta, por lo que se lleva a cabo una amplia revisi&oacute;n bibliogr&aacute;fica desde cuatro puntos de vista: vitamina E y propiedades antioxidantes, beneficios para la salud debidos a la ingesti&oacute;n de aceites vegetales, efecto de agentes externos y procesado sobre el contenido de vitamina E y t&eacute;cnicas anal&iacute;ticas utilizadas para su an&aacute;lisis.</p></font

Reaction Mechanism for Oxygen Reduction on Platinum: Existence of a Fast Initial Chemical Step and a Soluble Species Different from H2O2

The oxygen reduction reaction (ORR) on platinum in perchloric acid is studied under transient conditions at stationary and nonstationary electrodes. Only under these conditions, the presence of a fast initial chemical step in the mechanism, giving rise to a soluble, short-lived intermediate proposed to be the HO2* radical, is revealed by comparing experimental and calculated curves by numerical simulations of simple reaction schemes. The formation of this species and the existence of a zero-current cycle involving it would be the main reasons for the lack of reduction currents at potentials higher than the ORR reaction onset. Additionally, regardless of the exact subsequent steps after the initial chemical reaction, if HO2* is generated it would disproportionate to hydrogen peroxide, which implies that both species would be always produced during the ORR on Pt. The presence of HO2* and H2O2 would profoundly affect the durability of Pt-based catalysts and should be taken into account in the design of materials for fuel cell cathodes.The authors thank the Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP, Procs. 2013/16930-7 and 2014/23486-9), Brazil (A.G-M. and E.T.), and the Spanish MINECO through project CTQ2016-76221-P (FEDER) and GV through PROMETEOII/2014/013 (FEDER) (J.F.), for financial support

Role of the interfacial water structure on electrocatalysis: Oxygen reduction on Pt(1 1 1) in methanesulfonic acid

Most of electrocatalytic reactions occur in an aqueous environment. Understanding the influence of water structure on reaction dynamics is fundamental in electrocatalysis. In this work, the role of liquid water structure on the oxygen reduction at Pt(1 1 1) electrode is analyzed in methanesulfonic (MTSA) and perchloric acids. This is because these different anions can exert a different influence on liquid water structure. Results reveal a lower ORR electrode activity in MTSA than in HClO4 solutions and they are discussed in light of anion's influence on water structural ordering. From them, the existence of an outer-sphere, rate determining, step in the ORR mechanism is suggested.This work has been carried out under MINECO project CTQ2013-44083-P (Spain). APSR acknowledges the scholarship “Estudiantes sobresalientes de posgrado” at the UNAL and COLCIENCIAS National Doctoral Scholarship (567). MFS acknowledges the support of UNAL (Research Project 19030)