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8 Figuras, 1 Tabla, 2 Esquemas, The mechanism of CO and HCOOH electrooxidation in an acidic solution on carbon-supported Au–Pd core–shell nanoparticles was investigated by differential electrochemical mass spectrometry and in situ Fourier transform infrared (FTIR) spectroscopy. Analysis performed in nanostructures with 1.3 ± 0.1 nm (CS1) and 9.9 ± 1.1 nm (CS10) Pd shells provides compelling evidence that the mechanism of adsorbed CO (COads) oxidation is affected by structural and electronic effects introduced by the Au cores. In the case of CS10, a band associated with adsorbed OH species (OHads) is observed in the potential range of CO oxidation. This feature is not detected in the case of CS1, suggesting that the reaction follows an alternative mechanism involving COOHads species. The faradaic charge associated with COads oxidation as well as the Stark slope measured from FTIR indicates that the overall affinity and orbital coupling of CO to Pd are weaker for CS1 shells. FTIR spectroscopy also revealed the presence of HCOOads intermediate species only in the case of CS1. This observation allowed us to conclude that the higher activity of CS10 toward this reaction is due to a fast HCOOads oxidation step, probably involving OHads, to generate CO2. Density functional theory calculations are used to estimate the contributions of the so-called ligand and strain effects on the local density of states of the Pd d-band. The calculations strongly suggest that the key parameter contributing to the change in mechanism is the effective lattice strain., V.C. gratefully acknowledges the UK National Academy for their support through the International Newton Fellowship program (NF120002). D.P. and D.J.F. gratefully acknowledge funding from EPSRC (EP/K007025/1). J.J.L.H. is grateful for the Ph.D. scholarship partly funded by Sasol UK and NERC. E.P. acknowledges financial support from the Ministry of Economy and Competitiveness through Project ENE2014-52158-C2-2-R. D.J.F. is also grateful for the Research Fellowship from the Institute of Advanced Studies of the University of Bristol. TEM studies were performed at the University of Bristol Chemistry Imaging Facility with equipment funded by UoB and EPSRC (EP/K035746/1 and EP/M028216/1). We are grateful to Prof. Jeremy Sloan (University of Warwick, Coventry, U.K.) and Dr. Christoph Mitterbauer (FEI Co.) for the high-resolution TEM images of the CS1 nanoparticles. This work is part of the research network of the Deutsche Forschungsgemeinschaft FOR1376. E.S. acknowledges PIP-CONICET 112-201001-00411 and PICT 2012-2324; whereas P.M.Q. acknowledges PICT-2014-1084 (Agencia Nacional de Promoción Científica y Tecnológica, FONCYT, préstamo BID). A grant of computing time from the Baden-Württemberg grid is gratefully acknowledged. All the data presented in this paper can be freely accessed from the Bristol’s Research Data Repository (http://data/bris.ac.uk/10.5523/bris.1om4r04s216tn164tab9nfjyfg).

Fil: Martínez, Silvia Noemí. Universidad Nacional del Litoral. Facultad de Humanidades y Ciencias; Argentina. En el desarrollo de esta tesis nos centramos en (re)conocer los cambios epistemológicos que fueron surgiendo en la historia de la construcción del conocimiento y sus efectos en los ámbitos de transmisión. Todo ello como modo de comprender el paso desde un saber considerado único, inmutable, hacia otro dinámico, multifacético. Observamos un acercamiento hacia un cambio de visión en ámbitos académico-científicos, reconociendo la complejidad inherente del universo, para dejar de verlo “como una máquina”, a entenderlo “como una red”. Esta visión sistémica implica una renovación de vínculos entre el ser humano y la naturaleza. Se exploraron, además, campos que, desde el paradigma moderno, carecían de alguna relación, como arte y ciencia, señalando a artistas que se valieron de teorías y principios científicos como motivos de inspiración. Delineamos como alternativas de encuentro y diálogo de saberes, el cruce de umbrales entre disciplinas en busca de lo común, impulsando un corrimiento desde las certezas hacia lo novedoso en sentidos. Además, establecimos que los cambios en los paradigmas científicos implican cambios en la concepción del conocimiento, lo cual lleva a redefinir la ciencia, pensándola como práctica humana y cultural siempre en diálogo con la naturaleza. Esta visión epistemológica permitiría una representación compleja del universo más cercana a la realidad. Finalmente, consideramos que esta tesis se constituye en un intento de hallar nuevos lenguajes para la enseñanza de las ciencias -hasta hoy dogmática que permitan trascender la matriz hipotética-deductiva con la que históricamente fueron abordadas, concibiendo también válidas otras formas de producir el conocimiento. In order to comprehend the shift from a conception of knowledge considered exclusive and unchanging into a dynamic and multifaceted one, this thesis focuses on (re)acknowledging epistemological changes arising in the history of knowledge building and their effects on their communication environments. A change of perspective in the scientific and academic fields was observed, as an approach into recognising the complexity of the Universe in its being and into understanding it as a network instead of as a machine. This systemic view implies a renewal of bonds between Nature and the human being. The Arts and Science, fields with seemingly no relationship in the modern paradigm, were explored, highlighting artists that found in scientific theories and principles a source of inspiration. The moving through boundaries between areas of study in the search of what is shared was outlined as an alternative to the encounter and dialogue between forms of knowledge, encouraging a movement from known certainties into what is new in meanings. Furthermore, it was established that changes in scientific paradigms entail changes in the conception of Knowledge, which lead into a redefinition of Science as a human and cultural practice in continuous dialogue with Nature. This epistemological perspective would allow for a complex representation of the Universe closer to reality. Finally, this thesis is an attempt into finding new languages for teaching Sciences -to this day dogmatic-. Languages that allow to transcend the hypothetical-deductive matrix from which sciences were historically addressed, perceiving other ways of producing knowledge as valid.

Fil: Schulte, Erica Daniela. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. El presente trabajo de tesis abarca diferentes aspectos relacionados con el diseño de materiales y la posterior evaluación de la actividad electrocatalítica, utilizando como reacción prototipo una las etapas de la reacción de desprendimiento de hidrógeno (her). El estudio se realizó mediante la aplicación de herramientas de química computacional. Los materiales propuestos fueron nanoestructuras tipo conglomerados (2D) y alambres (1D) de Pd y Pt (de composición pura y bimetálica), depositados sobre un sustrato de Au(111). Inicialmente, se analizaron las nanoestructuras en fase gaseosa y cómo estas modificaron las propiedades electrónicas y geométricas luego de la deposición sobre el sustrato. Para el último caso, se analizó la estabilidad mediante el cálculo de la energía de enlace (entre las nanoestructuras y el sustrato), obteniéndose energías favorables en todos los casos. Para evaluar la actividad electrocatalítica de los materiales propuestos, se comenzó con el estudio la adsorción de un átomo de hidrógeno sobre diferentes sitios, a partir de cálculos basado en DFT, y se prosiguió con la aplicación de la Teoría de la Electrocatálisis para calcular la barrera energética de la etapa de Volmer (la cual forma parte del mecanismo de la her). En este aspecto, se han calculado diferentes parámetros de interés como las funciones de quimisorción, el nivel de energía del orbital 1s del hidrógeno, la energía de reorganización del solvente, entre otros, todos en función de la distancia del hidrógeno a las nanoestructuras. The present thesis work covers different aspects related to the design of materials and the subsequent evaluation of the electrocatalytic activity, using as a prototype reaction one of the stages of the hydrogen release reaction (her). The study was carried out by applying computational chemistry tools. The proposed materials were Pd and Pt (of pure and bimetallic composition) nanostructures (2D) and wires (1D), deposited on an Au(111) substrate. Initially, the gas-phase nanostructures and how they modified the electronic and geometrical properties after deposition on the substrate were analyzed. For the latter case, stability was analyzed by calculating the binding energy (between the nanostructures and the substrate), obtaining favorable energies in all cases. To evaluate the electrocatalytic activity of the proposed materials, we started with the study of the adsorption of a hydrogen atom on different sites by DFT, and continued with the application of the Theory of Electrocatalysis to calculate the energy barrier of the Volmer step (her mechanism). In this aspect, different parameters of interest have been calculated, such as the chemisorption functions, the energy level of the 1s orbital of hydrogen, the solvent reorganization energy, among others, all as a function of the distance of hydrogen to the nanostructures. Consejo Nacional de Investigaciones Científicas y Técnicas Agencia Nacional de Promoción de la Investigación, el Desarrollo Tecnológico y la Innovación Agencia Santafesina de Ciencia, Tecnología e Innovación Universidad Nacional del Litoral

La oxidación del monóxido de carbono adsorbido (COad) representa uno de los mayores problemas a resolver para mejorar el funcionamiento de las celdas de combustible que operan a baja temperatura. Su presencia, tanto sea como contaminante en el hidrógeno gaseoso de origen petroquímico o como resultado de la adsorción disociativa de moléculas orgánicas simples (ácido fórmico, metanol, etc.), es responsable de la disminución de la eficiencia del ánodo de la celda. En este contexto, se abordó el análisis del comportamiento del COad a partir del estudio de la reacción de electrooxidación de ácido fórmico (FAO) con el objeto de aportar evidencia acerca de la conducta del COad sobre distintos electrodos metálicos. A partir de este conocimiento detallado se desarrollaron electrodos bimetálicos caracterizados por la presencia de una juntura intermetálica, la que puede considerarse como un nuevo ámbito de reacción, a la vez que brinda la posibilidad de spillover de especies adsorbidas.El aspecto central de este estudio radicó en el empleo de una celda de flujo especialmente diseñada para producir un rápido desplazamiento del electrolito conteniendo la especie electroactiva por electrolito soporte y viceversa, manteniendo el circuito cerrado.En este marco se estudió la FAO sobre electrodos de platino, paladio, iridio, rodio y oro, los que exhibieron conductas marcadamente diferentes. Platino, iridio y rodio muestran que el proceso de adsorción disociativa del ácido fórmico conduce a la formación de COad, lo cual no se observó en el paladio y el oro. En base a los resultados obtenidos, que incluyen la evaluación del potencial a circuito abierto, voltamperometría cíclica, cronoamperometría, stripping voltamperométrico, además de otras técnicas de caracterización fisicoquímica y de información espectroscópica conocida, se pudieron establecer los mecanismos de reacción sobre los cinco metales y se evaluaron los parámetros cinéticos elementales en platino y paladio.Sobre la base del conocimiento de la FAO sobre los electrodos metálicos y empleando el concepto de corriente de exceso previamente desarrollado ennuestro laboratorio, se estudió la reacción sobre los electrodos bimetálicos paladio-platino, paladio-oro, rodio-oro y platino-oro. Los resultados obtenidos ponen en evidencia un conjunto de hechos no considerados y/o tenidos en cuenta hasta el presente en los trabajos reportados en la bibliografía. Una de las conclusiones está relacionada con la importancia de reconocer que la cinética de una reacción que tiene lugar sobre un electrodo bimetálico, que presenta superficies expuestas de ambos metales, no puede ser descripto a través de un único mecanismo de reacción y menos aún con un conjunto único de parámetros cinéticos. En el mismo sentido, se mostró que no necesariamente los intermediarios adsorbidos sobre uno de los metales deben estar presentes en el otro metal. Este hecho origina una serie de consecuencias nunca antes planteadas ni analizadas, que obligan a repensar el análisis e interpretación cinética de reacciones electrocatalizadas por electrodos bimetálicos. Una de ellas es que el mecanismo de reacción podriá ser diferente sobre cada uno de los metales. Otra consecuencia específica de los resultados obtenidos es que ciertos metales que poseen buena actividad electrocatalítica para la FAO, pierden esta cualidad al constituir un electrodo bimetálico. Un ejemplo es el caso del paladio, sobre cuya superficie no se forma COad vía adsorción disociativa del acido fórmico. Sin embargo, los resultados obtenidos sobre el electrodo de Pt-Pd indican la presencia de la especie COad sobre el paladio, proveniente del platino a través del fenómeno de spillover en la juntura intermetálica. Contrariamente, el spillover de especies intermediarias desde un metal hacia el otro puede promover el aumento de la actividad electrocatalítica, como es el caso del sistema Au-Pd. Todos los sistemas estudiados fueron analizados e interpretados en base a las conductas y mecanismos derivados de los metales puros. Fil: Luque, Gisela Carina. Universidad Nacional del Litoral. Instituto de Química Aplicada del Litoral. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Química Aplicada del Litoral.; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Programa de Electroquímica Aplicada e Ingeniería Electroquímica; Argentina

Increasing demand for clean, globally available energy, provokes the development of alternative or nonconventional energy storage sources with higher energy density and power delivery. Therefore, supercapacitors have received great attention in both academic and industrial research. In addition, supercapacitors are promising new sources of energy in the future energy technology. Hence, rapid progress has been made to understand their fundamentals and applicable aspects. Supercapacitors, also known as ultracapacitors, bridge the gap between batteries and con- ventional capacitors, which means that supercapacitors can accept and deliver charge much faster than batteries, and can store 10 to 100 times more energy per unit volume than fuel cells. Su- percapacitors are well known not only because of their huge energy density, but also due to their long shelf and good cyclic ability. The particular properties of supercapacitors are due to utiliza- tion of electrode materials with very high porosity, and also the specific mechanism of charge storage. In general, there are two fundamental chemical and physical mechanisms for energy storage. In chemical mechanism the charges are released through oxidation-reduction reaction. However, in the physical mechanism the electrical energy is stored physically with electrostatic interaction, while no chemical and phase changes occur. Hence, according to theses charge storage mechanisms supercapacitors are divided into three main groups: electric double layer capacitors (EDLCs), pseudocapacitors and hybrid capacitors. Each of these supercapacitors has its own ad- vantages and disadvantages. These three different kind of supercacaitors are distinguished by their charge storage mechanism and also their electrode materials. Electrical double layer capacitors store the charge based on physical mechanism, and also various types of carbon are used as electrode material. Pseudocapacitors save energy via electro- chemical redox reactions. Besides, these capacitors utilize metal oxides and conducting polymers as electrode material. Hybrid capacitors are another class of supercapacitors, which are constructed of two different types of electrode materials. Therefore, the mechanism of energy storage is a com- bination of both chemical and physical mechanisms. The most used electrode materials in these supercapacitors are a composition of carbon-based materials with either conducting polymers or metal oxide materials. In this work electrical double layer capacitors have captured our attention because of both their interesting energy storage mechanism and also their electrode materials. Electrode material is one of the most important factors in the performance of an electro- chemical energy storage device. Therefore, innovation of new electrode materials is one of the most attractive topics in recent investigations. Especially carbon based electrodes such as carbon nanofibers, activated carbon, carbon nanotubes (CNTs) etc. with their porous structure can pro- vide very huge surface area, consequently immense capacity. Among the examined carbon based materials carbon nanotubes are one of the most interesting because of their unique physical and chemical properties. In fact, special properties of carbon nanotubes such as individual tubular structure, very high chemical stability, low resistivity, high thermal and electrical conductivity and enormous surface area make them good candidates for electrode material in electrical double layer capacitors. Carbon nanotubes are divided into three main groups such as zigzag, armchair and chi- ral tubes. Based on their electronic structure, carbon nanotubes can have metallic or semimetallic characteristic. As mentioned above the huge capacity of carbon materials is due to their massive surface area. Furthermore, in the case of carbon nanotubes both the inner and outer walls can be available for electrolyte ions. At first it was thought, that very narrow pores do not participate in the forma- tion of double layer and energy storage. However, experimental investigations proved, that very narrow pores (lower than 1nm size) not only participate in energy storage, but also exhibit an enor- mous increase of capacitance. Later, theoretical findings showed that the image charge between ion and pore wall screen the repulsion between the ions. This leads to a denser packing of ions, consequently increasing the electrode capacitance. In this work we have studied ion intercalation into carbon nanotubes with diameters lower than 1nm as electrode material by density functional theory. All the calculations have been done using the VASP package. The idea of this work is in that we have imagined carbon nanotubes as electrode materials immersed in solution. Hence, the electrolyte ions try to penetrate into the carbon nanotubes. This work is divided into four parts, which are as follows: In the first part, we have selected truncated carbon nanotubes or carbon nanorings, whoese ends are saturated with hydrogen atoms. In particular, the truncated carbon nanotubes are include the (6,0), (8,0), (10,0) and (12,0) carbon nanotubes. As electrolyte ions alkali (Li, Na and Cs) and halogen (Cl, Br and I) atoms have been tried. Meanwhile, we have neglected the presence of solvent or any counterpart. After simulation it was realized that all the alkali atoms have lost one electron, and also the halogen atoms have obtained one more electron, and also the stable position of all the ions is in the center of the tubes. The results have shown that the surrounding tubes screen the ionic charge very effectively, thereby the ion-ion interactions are strongly reduced, which explains, why narrow tubes store charge more effectively than wider one. We have calculated the insertion energies of the atoms into the tubes and understood that for each atom the diameter of the tube has to be optimized. In the second part of the work, we extended the model of short nanotubes to infinite ones. In particular, we have chosen the (6,2)CNT, the (6,3)CNT, the (8,0)CNT and the (5,5)CNT as electrode material. Among the presented carbon nanotubes the (6,2)CNT and the (8,0)CNT are semimetallic, while the (5,5)CNT and the (6,3)CNT are metallic. Like in the previous work we have inserted alkali (Li, Na and Cs) and halogen (F, Cl, Br and I) atoms into the carbon nanotubes. The results have shown that the atoms were fully ionized. The charge exchange with the CNTs affects the band structure, and turns those tubes that were originally semiconductors into conductors. None of the ions is adsorbed chemically, their position inside the tube and their energies of adsorption are determined by a competition between electrostatic image interactions, which favor a position at the wall, and Pauli repulsion. In models for charge storage it is often assumed that in small tubes the ions are at the center, but we have found several cases where small alkali ions are positioned near the wall. We have also investigated the screening of the Coulomb potential along the axis of the tubes. In particular we wanted to see if there is a difference between semiconducting and conducting CNTs. Within the accuracy of our calculations we found no difference in the screening, because the charge transfer has made the non-chiral tubes conducting. In the third part of this work, we have investigated insertion of alkali and halogen atoms into nitrogen doped (N-doped) carbon nanotubes. Here, the (8,0)CNT and the (5,5)CNT have been chosen as electrode material. The results have shown that N-doped carbon nanotubes are less stable than the pure ones, and also the atoms were fully ionized. The position of the ions in the carbon nanotubes exhibits contradictory behavior in the (8,0)CNT than the (5,5)CNT. In fact, in the former one the ions have high repulsion from the impurity area and try to get away as far as possible. This effect is stronger in the case of small ions like Li+. However, in the (5,5)CNT the ions get closer to the nitrogen area. This behavior is caused by the difference in the spin density of carbon nanotubes. In other words, the spin density is more localized in the N-doped (8,0)CNT than the N- doped (5,5)CNT. Therefore, it causes big repulsion with the inserted ions. The nitrogen doping and charge exchange with ions affect the band structure of carbon nanotubes. Actually, substitution of nitrogen and insertion of alkali atom keep the tubes conducting. However, intercalation of halogen atoms causes both tubes to become semiconducting. We also have calculated insertion energy of ions in the N-doped carbon nanotubes. The results have shown that insertion of the ions is more favorable in the N-doped carbon nanotubes than in the pure ones. In the fourth part of the work, we have taken into account the presence of counterions. For this purpose we have tried insertion of alkali halide monomers (LiF, LiCl and NaCl), a chain of NaCl in nanotube, as well as presence of water molecules with NaCl monomer in a carbon nanotube. Therefore, the (5,5)CNT as electrode material has been chosen. In all the investigated systems, the ions and the molecules are not chemically bound to the carbon nanotube wall. In the case of alkali halide monomers there is no strong charge transfer with the nanotube. However, for the chain of NaCl this interaction is stronger, while the main charge transfer is between the alkali and halide ions in the chain. Water does not exchange charge with the nanotube. Nonetheless, it tries to hydrate the alkali and halide ions confined in the tube.

Fil: Cabana García, Nancy Cecilia. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina. Se presentan resultados de cálculos teóricos de las energías de interacción, geometrías de enlaces, densidades de carga electrónica y modos de vibración del tolueno adsorbido en mordenita dopada con sodio. Los cálculos se basaron en técnicas de la teoría de la funcional densidad (DFT) utilizando los códigos fireball y gaussian. Se pudo obtener por primera vez una estabilización completa de cuatro modelos diferentes para la estructura geométrica y electrónica de la mordenita modificada. Para el cálculo de la energía de interacción se debió calcular primero la estructura sin sodios, luego con ellos y finalmente con el tolueno adsorbido en diferentes posiciones. Los resultados teóricos indican que la principal interacción del tolueno con la zeolita es entre los electrones "pi" del anillo aromático y la base de Lewis generada por la incorporación del catión a la que se suma también una interacción entre el grupo metilo con un sitio de oxígeno de la zeolita, que los picos principales de vibración del doble enlace del tolueno se corren a frecuencias menores y que uno de ellos directamente desaparece en la situación de adsorción. Estos resultados están en un todo de acuerdo con resultados experimentales previos obtenidos por el grupo de trabajo y por lo tanto se constituyen en una sólida base para progresar en el diseño de nuevos materiales con las condiciones de adsorción deseadas. Theoretical calculations of binding energy, bonding geometries, electronic density of states and vibrational modes of toluene adsorbed on sodium-doped mordenite are presented. The codes fireball and gaussian based on Density functional Theory were used. An stabilization of the structure of four different models for the mordenite was reached for the first time. The results indicate that the main interaction of the toluene with the matrix is between pi-electrons of the aromatic ring and the Lewis basis which appears for the doping with cation. Besides, there is an important interaction between the methyl group with an particular oxigen of the structure. Regarding the vibrational modes, the main vibrations of the doble bond in the aromatic ring are shifted towards minor frequencies and one of them vanishes completely in the adsorption situation. All of the results are in very good agreement with the experimental data and, therefore, become a solid support for future investigations about the design of this new materials.

Fil: Bonazza, Horacio Lisandro. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina Se realizó un estudio cinético teórico-experimental de la reacción del electrodo de hidrógeno (HER) en condiciones de altas velocidades de transporte de masa a través de dos estrategias: la utilización de ultramicroelectrodos y la aplicación de microscopía electroquímica de barrido. En base a formalismos teóricos rigurosos previos se desarrollaron ecuaciones para interpretar la HER sobre ultramicroelectrodos en un amplio rango de condiciones de pH. El mismo incluye la participación del agua como reactivo/producto de la HER y el modelado del transporte de masa de protones y oxidrilos. Esto permitió disponer de dependencias teóricas completas de la densidad de corriente con el sobrepotencial y el pH, y de la resistencia de polarización con la densidad de corriente límite difusional anódica y el pH. Estas ecuaciones permitieron calcular el conjunto completo de velocidades de equilibrio de las etapas elementales de la HER sobre ultramicroelectrodos de rodio y de iridio de diferentes tamaños. Paralelamente, la Tesis se enfocó en los aspectos prácticos de la implementación de la técnica SECM, lo cual involucró el montaje de un instrumento SECM y el desarrollo de un método de fabricación de tips de metales nobles con tamaños micro- y submicro-métricos. Se emprendió un estudio teórico-experimental de la HER y para ello se desarrolló un formalismo teórico que permite realizar un análisis completo del mecanismo de la HER a partir de resultados SECM operando en el modo feedback. El modelo fue contrastado con resultados de simulaciones realizadas por métodos numéricos y con resultados experimentales obtenidos sobre Pt. In this work a theoretical and experimental kinetic study of the hydrogen electrode reaction (HER) under high mass transport rates through two strategies was performed: ultramicroelectrodes and application of scanning electrochemical microscopy. Based on previous rigorous theoretical formalism, some equations were developed to interpret HER reaction on ultramicroelectrodes on a wide range of pH conditions. This formalism includes water as reactant / product of the HER reaction and modeling of mass transport of hydroxyl and proton ion. Thus the complete theoretical dependency of the current density with the overpotential and the pH was obtained, and the polarization resistance with the anode diffusional limit current density and pH. These equations were used to calculate the full set of equilibrium rates of the elementary steps of HER reaction on different radii rhodium and iridium ultramicroelectrodes. Similarly, this work has focused on the practical implementation of the SECM technique, which involved the assembly of a SECM instrument and the development of a method of making noble metal tips with micro-and submicro-metric sizes. A theoretical and experimental study of the HER was undertaken through a theoretical formalism that allows a complete analysis of the mechanism of HER reaction results from SECM technique operating in the feedback mode. This model was compared with results of simulations by numerical methods and experimental results on Pt metal. Agencia Nacional de Promoción Científica y Tecnológica Universidad Nacional del Litoral Consejo Nacional de Investigaciones Científicas y Técnicas

Fil: Arce, Mauricio Damián. Universidad Nacional del Litoral. Facultad de Ingeniería Química; Argentina The present thesis work covers different aspects related to the kinetics of the oxygen reduction reaction (orr), with the aim to provide new knowledge concerning to the understanding of one of the main reactions in the electrochemistry field. In particular, the studied materials cover the noble metal group. The principal tool used for the orr study consists of systems with high mass transport rates, as a consequence, several synthesis and characterization methods were developed for the fabrication of microelectrodes (MEs). In order to be able to interpret the results, a rigorous kinetic model was proposed, which takes into account the different reaction routes. The deduced equations were used for simulation and fitting of polarization curves for the orr, which allowed for the access of the kinetic elemental parameters that governs the reaction for each material. Bimetallic electrodes were also studied, being a very interesting configuration taking into account that some metal combinations present an enhancement in the electrocatalytic response towards the orr (synergetic effect). In this case, besides the conventional techniques applied to the MEs, the study was complemented with theoretical quantum calculations using the Density Functional Theory (DFT). This provides information about the structural and electronic modifications on the electrode material with the different intermediate species involved in the reaction mechanism. The experimental and theoretical results allow to have a comprehensive idea of the synergetic mechanism between the materials. El presente trabajo de tesis abarca diferentes aspectos relacionados con la cinética de la reacción de reducción de oxígeno (orr) con la finalidad de aportar nuevos conocimientos que contribuyan al entendimiento de una de las reacciones de mayor importancia en el área de la electroquímica. En particular los materiales estudiados en esta tesis comprenden el grupo de los metales nobles. La principal herramienta utilizada para el estudio de la orr la constituyeron sistemas que presentaran elevadas velocidades de transporte de masa, desarrollándose para ello variados métodos de síntesis y caracterización de microelectrodos (MEs) con diferentes características. Con el objetivo de poder interpretar los resultados obtenidos, se propuso un modelo cinético riguroso que contempla las diferentes rutas de reacción. Las ecuaciones deducidas fueron utilizadas para simular y ajustar curvas de polarización para la orr, lo que permitió acceder a los parámetros cinéticos elementales que gobiernan la reacción para cada material. Por otra parte, también se estudiaron electrodos bimetálicos, siendo esta configuración de gran interés ya que ciertas combinaciones presentan una mejora en la actividad electrocatalítica hacia la orr (efecto sinérgico). En este caso se complementaron las técnicas convencionales aplicadas a MEs mediante estudios teórico-cuánticos haciendo uso de la teoría de la funcional densidad (DFT). Esto permitió obtener información en cuanto a modificaciones estructurales y electrónicas del material de electrodo con las diferentes especies intermediarias presentes en el mecanismo de reacción. El complemento entre el análisis experimental y el teórico permiten tener una idea global del mecanismo de sinergia entre los materiales. Agencia Nacional de Promoción Científica y Tecnológica Consejo Nacional de Investigaciones Científicas y Técnicas