1,721,392 research outputs found
A sublattice-model isotherm for the competitive coadsorption of hydrogen and bromide on a Pt(100) electrode
No full textPrevious work demonstrated that the Frumkin isotherm is inadequate to model the competitive coadsorption of species with different saturation coverages, such as hydrogen and bromide coadsorption on Pt(100) [N. Garcia-Araez et al., J. Electroanal. Chem., 2006, 588, 1]. Therefore, Monte Carlo simulations were necessary to determine meaningful values of the microscopic parameters (namely, energies of adsorption and interaction). In the present work, an alternative analytical isotherm is developed, by taking into account the occupation of two sublattices, which together compose the whole lattice of adsorption sites. Despite its relatively simple mathematical form, this isotherm presents, under certain conditions, a significant improvement over the classical Frumkin isotherm for the modeling of competitive adsorption processes, thus providing a closer agreement with results from Monte Carlo simulations. Finally, it is demonstrated that the sublattice-model isotherm will be generally applicable to systems in which the formation of segregated adlayers, whose structure is not explicitly taken into account in the model, is energetically unfavorabl
CO electroxidation on gold in alkaline media: a combined electrochemical, spectroscopic and DFT study
No full textSelf-promotion mechanism for CO electrooxidation on gold: a combined electrochemical, spectroscopic and DFT study
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Electrocatalysis of the nitrite reduction : a mechanistic study
Full text linkThis project has dealt with the mechanistic study of the electrocatalytic nitrite reduction, the selectivity-determining step of nitrate reduction. Nitrate is a polluting ion targeted by wastewater remediation; electrochemistry strives to achieve selectivity to harmless products (N2). A multi-pronged approach has been followed, aimed at establishing the influence of several variables (electrocatalyst material, surface structure, pH and electrode potential) on the catalytic activity and the product distribution, which has been determined with in situ analytical techniques (mass spectrometry and infrared spectroscopy). The molecular underpinnings of nitrite reduction have thereby been unravelled for transition metals, showing that an optimal catalytic performance is achieved when metals intermediate affinities to reaction intermediates (Sabatier Principle). The all-important concept of structure sensitivity also applies to nitrite reduction at Pt electrodes, although only in alkaline media: a Pt(100) single-crystal is the sole Pt surface able to achieve the desired direct conversion of nitrite into 100% N2. Such selectivity is unparalleled for a simple monometallic surface and is an outstanding finding. Additionally, the nitrite-reducing performance of bio-inspired catalysts, (electroactive metalloporphyrins) was investigated. A further side-project of this PhD thesis has also been the electrochemical characterization of preferentially-oriented cuboid Pt nanoparticles synthesized with the innovative __cathodic corrosion__.UBL - phd migration 201
The electrocatalytic oxidation of ethanol studied on a molecular scale
Full text linkThis thesis describes the results of the fundamental research on the electro-oxidation of ethanol. In addition, the oxidation of intermediates in the ethanol electro-oxidation reaction, such as acetaldehyde and adsorbed CO, has also been studied. The goal of this research is to provide deeper insight into the molecular level understanding of the mechanism, and how various operational parameters affect this mechanism. With these insights, the development of low temperature direct ethanol fuel cells (DEFC) can be advanced, since, ultimately, the goal of fundamental catalysis research is the rational design of new catalysts, for which the understanding of molecular mechanisms is of essential importance. The mechanism of the electro-oxidation reaction is investigated using electrochemical techniques, such as cyclic voltammetry and chronoamperometry, as well as in situ characterization techniques, such as surface enhanced Raman spectroscopy (SERS), Fourier transform infrared spectroscopy (FTIR) and online electrochemical mass spectrometry (OLEMS).UBL - phd migration 201
Surface-structure dependencies in catalytic reactions
Full text linkHeterogeneous catalysis is very important for industrial applications and the environment. It is known that precious metals, such as Pd and Pt, can be good catalyst materials for various reactions. However, these metals are expensive and their catalytic action is not yet completely understood. In the search for better and cheaper materials, more fundamental knowledge is necessary. We use ultra-high vacuum techniques and well-ordered Pd and Pt single crystals to further investigate the oxygen dissociation process and the interaction of water with deuterated surfaces.NRSC-CatalysisUBL - phd migration 201
Water on well-defined platinum surfaces : an ultra high vacuum and electrochemical study
Full text linkWe have investigated the dissociation state of water on platinum electrodes. The desorption of D2, O2, and H2O is influenced significantly by the presence of step sites and the geometry of those sites. Under UHV conditions OH groups can be formed on Pt(111) by pre-covering the surface with O adatoms, causing water to dissociate. We have shown that on stepped platinum surfaces OHad might not be as readily formed as one would assume based on the energetics of OH adsorption alone. Even though the Pt(533) and Pt(553) surfaces have similar geometries, the hydrophobicity on the deuterated surface is surprisingly different: on D/Pt(533) the surface is hydrophobic with water clustering at steps, whereas the entire surface is wet on D/Pt(553). Under electrochemical conditions we show that in spite of the similar looking cyclic voltammograms, the kinetics of underpotential deposited hydrogen are significantly different in acidic and alkaline media. In alkaline media the ad- and desorption process is slow, whereas it is very fast in acidic media. We have pointed out three discrepancies in the current interpretation of the blank cyclic voltammetry of stepped platinum surfaces and propose a co-adsorption model that accounts for these discrepancies.UBL - phd migration 201
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