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1
Lively, Treise. "Ethanol fuel cell electrocatalysis : novel catalyst preparation, characterization and performance towards ethanol electrooxidation." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602560.
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Williams, Mario. "Characterization of platinum-group metal nanophase electrocatalysts employed in the direct methanol fuel cell and solid-polymer electrolyte electrolyser." Thesis, University of the Western Cape, 2005. http://etd.uwc.ac.za/index.php?module=etd&.
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Ying, Qiling. "Preparation and characterization of highly active nano pt/c electrocatalyst for proton exchange membrane fuel cell." Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_3791_1188474883.
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<p>Catalysts play an essential role in nearly every chemical production process. Platinum supported on high surface area carbon substrates (Pt/C) is one of the promising candidates as an electrocatalyst in low temperature polymer electrolyte fuel cells. Developing the activity of the Pt/C catalyst with narrow Pt particle size distribution and good dispersion has been a main concern in current research.</p>
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In this study, the main objective was the development and characterization of inexpensive and effective nanophase Pt/C electrocatalysts. A set of modified Pt/C electrocatalysts with high electrochemical activity and low loading of noble metal was prepared by the impregnation-reduction method in this research. The four home-made catalysts synthesized by different treatments conditions were characterized by several techniques such as EDS, TEM, XRD, AAS, TGA, BET and CV.</p>
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Pt electrocatalysts supported on acid treatment Vulcan XC-72 electrocatalysts were produced successfully. The results showed that Pt particle sizes of Pt/C (PrOH)x catalysts between 2.45 and 2.81nm were obtained with homogeneous dispersion, which were more uniform than the commercial Pt/C (JM) catalyst. In the electrochemical activity tests, ORR was confirmed as a structure-sensitive reaction. The Pt/C (PrOH/pH2.5) showed promising results during chemically-active surface area investigation, which compared well with that of the commercial standard Johnson Matthey Pt/C catalyst. The active surface area of Pt/C (PrOH/pH2.5) at 17.98m2/g, was higher than that of the commercial catalyst (17.22 m2/g ) under the conditions applied. In a CV electrochemical activity test of Pt/C catalysts using a Fe2+/Fe3+ mediator system study, Pt/C (PrOH/pH2.5) (67mA/cm2) also showed promise as a catalyst as the current density is comparable to that of the commercial Pt/C (JM) (62mA/cm2).</p>
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A remarkable achievement was attained in this study: the electrocatalyst Pt supported on CNTs was synthesized effectively. This method resulted in the smallest Pt particle size 2.15nm. In the electrochemically-active surface area study, the Pt/CNT exhibited a significantly greater active surface area (27.03 m2/g) and higher current density (100 mA/cm2) in the Fe2+/Fe3+ electrochemical mediator system than the other home-made Pt/C catalysts, as well as being significantly higher than the commercial Pt/C (JM) catalysts. Pt/CNT catalyst produced the best electrochemical activities in both H2SO4 and K4[Fe(CN)6] electrolytes. As a result of the characteristics of Pt/CNTï¼it can be deduced that the Pt/CNT is the best electrocatalyst prepared in this study and has great potential for use in fuel cell applications.</p>
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Hui, Chiu Lam. "Surfactant stabilized nanoscale electrocatalysts for fuel cell applications /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?EVNG%202005%20HUI.
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Haslam, Gareth Eric. "Ni-C and WC materials as fuel cell electrocatalysts." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610113.
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Fahy, Kieran. "Base-material electrocatalysts for oxygen reduction in low temperature fuel cells." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707964.
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Rees, Eric John. "The role of synthesis conditions for metal-carbide electrocatalysts in fuel cells." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609023.
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Kavanagh, R. J. "A computational study of anode electrocatalysis in direct ethanol fuel cells." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678702.
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Density Functional Theory calculations are employed in the investigation of the ethanol oxidation reaction (EOR) at the anode of Direct Ethanol Fuel Cells (DEFC), with a view to mechanistic understanding of the reaction pathways, determination of the factors governing the onset potential of activity and selectivity towards C02, and ultimately the design of an optimal electrocatalyst in these regards. The lowest energy pathway of ethanol decomposition on platinum is identified and it is found that the reaction kinetics do not significantly vary with catalyst morphology. The aqueous medium is found to somewhat facilitate all reaction pathways. Surface hydroxyl is found to oxidise ethanol to acetaldehyde. Surface atomic oxygen is found to selectively oxidise adsorbed carbon monoxide to carbon dioxide. The onset potentials of surface hydroxyl and atomic oxygen on platinum are calculated to be in good agreement with experimental data. It is determined that onset potentials of < 0.1 V vs. SHE will result in inactive hydroxyls, while an onset potential of < 0.2 V results in inactive surface atomic oxygen, providing a target for catalyst optimisation. Onset of EOR is found to occur at potentials between 0.4 V and 0.5 V earlier on a range of platinum tin catalysts than on platinum, and Pt3Sn is found to be kinetically the best example of such a catalyst These findings are in good agreement with experimental observations. The addition of rhodium to platinum is found to result in a hydroxyl onset potential below the 0.1 V threshold for activity, and the near-optimal onset potential of surface atomic oxygen, resulting in excellent selectivity towards C02. However, the stability of the hydroxyl species delays the formation of atomic oxygen and so delays the onset of ethanol oxidation activity to an unacceptably high degree. This effect is believed to be general to metallic systems.
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Barron, Olivia. "Catalyst Coated Membranes (CCMs) for polymerelectrolyte Membrane (PEM) fuel cells." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_4757_1307336145.
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<p>The main objective of this work it to produce membrane electrode assemblies (MEAs) that have improved performance over MEAs produced by the conventional manner, by producing highly efficient, electroactive, uniform catalyst layers with lower quantities of platinum electrocatalyst. The catalyst coated membrane (CCM) method was used to prepare the MEAs for the PEM fuel cell as it has been reported that this method of MEA fabrication can improve the performance of PEM fuel cells. The MEAs performances were evaluated using polarisation studies on a single cell. A comparison of polarisation curves between CCM MEAs and MEAs produced in the conventional manner illustrated that CCM MEAs have improved performance at high current densities (><br>800 mA/cm2).</p>
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Feng, Chunhua. "Microfabrication-compatible synthesis strategies for nanoscale electrocatalysts in microfabricated fuel cell applications /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CENG%202007%20FENG.
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Kumar, Sachin. "Electrocatalysis at Metal Nanoparticles." Miami University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=miami1218138524.
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Ziegelbauer, Joseph M. "Fundamental aspects of oxygen reduction reaction on non-platinum electrocatalysts an electrochemical and in situ X-ray absorption spectroscopy study : a dissertation /." View dissertation online, 2007. http://hdl.handle.net/2047/d10016211.
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Sode, Aya. "Electrocatalysis on PtZn surface - fundamental studies and the applications in PEM fuel cells." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/5582.
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The PtZn alloy was characterized and studied as a possible candidate for proton exchange membrane fuel cells (PEMFCs). Zn was electrochemically deposited on a bulk Pt substrate and the alloy was spontaneously formed at ambient conditions, as confirmed by Auger electron spectroscopy (AES). PtZn decreased the oxygen reduction reaction (ORR) overpotential by 30 mV with respect to that measured for Pt. The alloy was also prepared in a similar manner on a membrane electrode assembly (MEA) and studied in a single stack fuel cell. The PtZn MEA also showed an improved performance compared to the Pt MEA. Carbon monoxide oxidation catalysis was also investigated. Zn modification of a Pt substrate makes the resulting surface rough, and the roughness was compensated through the measurement of capacitance. Although, in this case, Zn modification did not enhance the catalytic activity compared to Pt, cycling the potential in a CO saturated acidic solution made the PtZn surface smoother and more Pt-rich. The ORR catalytic activity was also compared to Pt with equivalent roughness. PtZn showed enhancement in the kinetics of the reaction, indicating Zn modification had impact on improving the ORR catalytic activity beyond the roughness effect. The PtZn surface becomes Zn-rich after cycling the potential in an oxygen saturated acidic solution. The stability of the alloy under fuel cell operating conditions was also studied. PtZn nanoparticles were formed on glassy carbon substrates and the surface and bulk alloy compositions were determined before and after the alloy was polarized in an oxygen saturated acidic solution. Approximately 18% of Zn originally present in the alloy was lost after 40 hours of polarization at 0.8 V vs. RHE. It was also confirmed PtZn particles adhere well to carbon and were free from sintering effects. The cumulative results presented support that the PtZn alloy is thus a promising candidate for the cathode of PEMFCs.
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Chin, Xiao Yao. "Ni-C electrocatalysts for hydrogen oxidation in low-temperature acidic fuel cells." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610637.
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Coleman, Eric James. "Robust Platinum-Based Electrocatalysts for Fuel Cell Applications." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437484946.
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Sneed, Brian Thomas. "Synthesis of Strained Metal Nanocrystal Architectures for Energy Conversion Electrocatalysis." Thesis, Boston College, 2015. http://hdl.handle.net/2345/bc-ir:104488.
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Thesis advisor: Chia-Kuang F. Tsung<br>Thesis advisor: Dunwei Wang<br>In order to understand the lattice strain effect and its relationship to size, shape, composition, and catalytic performance, novel well-defined nanocrystal archetypes were designed and synthesized by taking advantage of wet chemical, seed-mediated (mild) reduction routes developed by our lab. First, the current synthesis challenges are addressed in creating smaller monometallic shape-controlled metal nanocrystals, and novel cuboctopods via a hybrid nanoparticle stabilizer. A look at the relationship between lattice strain and morphology is then shown in a single-component system, where still new features have been observed for the first time by the traditional technique of powder x-ray diffraction. Synthesis methods for differently strained Pd surfaces are described and catalysis by these surfaces is discussed. Finally, studies of the synthesis, characterization, electrocatalytic activity, and restructuring of novel and more sophisticated strained architectures are presented: core-island-shell nanocrystals, phase-segregated nanoboxes, island nanoframeworks, and core-sandwich-shell nanoparticles. Lattice strain and composition effects were studied in carbon monoxide, small alcohol, and formic acid electrocatalytic oxidations as well as in oxygen reduction, the latter of which, governs the commercial viability of automotive fuel cells, a sustainable energy and zero-emission technology. Here it is demonstrated how a tunable thickness of Ni sandwich layers can be used to improve catalytic performance by increasing lattice strain on the Pt surface. The sandwich archetype offers a new platform for the investigation of lattice strain and could be a promising, industrially relevant, catalyst design concept, to help address the need for a more sustainable energy future. The results help paint a new picture of catalysis by metal nanocrystals; one which brings lattice strain to the forefront of the discussion, as an important parameter for further study and for use in developing higher-performing catalysts<br>Thesis (PhD) — Boston College, 2015<br>Submitted to: Boston College. Graduate School of Arts and Sciences<br>Discipline: Chemistry
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Blavo, Selasi Ofoe. "Model Pt- and Pd-based Electrocatalysts for Low Temperature Fuel Cells Applications." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4639.
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In the search for alternative energy technologies, low temperature fuel cells continue to feature as technologies with the most promise for mass commercialization. Among the low temperature fuel cells, alkaline and proton exchange membrane fuel cells are the most popular. Alkaline fuel cells have typically been used for water generation as well as auxiliary power for space shuttles. Their bulkiness however makes them undesirable for other applications, especially in automobiles, where there is a great demand for alternative technologies to internal combustion engines. Proton exchange membrane fuel cells on the other hand possess numerous qualities including their compact size, high efficiency and versatility. Their mass implementation has however been delayed, because of cost among other reasons. Most of this cost is owed to the Pt/C catalyst that accounts for about half of the price of the PEM Fuel Cell. This catalyst is used to drive the sluggish oxygen reduction reaction that occurs at the cathode of the PEM Fuel Cell.
To overcome this obstacle, which is to make PEM Fuel Cell technology more affordable, reducing the amount Pt has traditionally been the approach. Another approach has been to find new ideal catalyst-support combinations that increase the intrinsic activity of the supported material. One more strategy has been to find lower cost alternative materials to Pt through synthetic and kinetic manipulations to rival or exceed the current oxygen reduction reaction activity benchmark.
To this end, Palladium has garnered significant interest as a monometallic entity. Its manipulation through synthetic chemistry to achieve different morphologies - which favor select lattice planes - in turn promotes the oxygen reduction reaction to different degrees. In bimetallic or, in more recent times multimetallic frameworks, geometric and ligand effects can be used to form ideal compositions and morphologies that are synergistic for improved oxygen reduction reaction kinetics.
In this dissertation, we have explored three different approaches to make contributions to the catalysis and electrocatalysis body of literature. In the first instance, we look at the influence of ligand effects through the active incorporation of a PVP capping agent on the stability of ~3nm Pt NPs. Washed (no capping agent) and unwashed (with capping agent) batches of NPs were evaluated via cyclic voltammogram analyses to evaluate differences there might be between them. It was found that the current density measurements for unwashed particle batches were higher. This increase in current density was attributed to the monodentate and bidentate ligand bonding from the PVP, which increased as a function of cycle number and plateaued when the PVP was completely decomposed. The complete decomposition of PVP during the CV experiment was estimated to occur around 200 cycles.
The remaining portion of the dissertation explores the electrocatalytic properties of Palladium based NPs. The first instance, a monometallic study of Palladium cubes and dendrites was aimed at building on a recent publication on the enhanced ORR activity that was achieved with a PdPt bimetallic dendrite morphology. In our work, we sought to isolate the dendritic morphology properties of the monometallic Pd composition in order to understand what advantages could be achieved via this morphology. Pd cubes were used as a comparison, since they could be generated through the combination of a similar set of reagents simply by switching the order of addition. It was found that while there was no significant variation in the ORR activity as a function of morphology / shape, there was an interesting interaction between hydrogen and the palladium NPs in the hydrogen oxidation region that varied as a function of shape. This led to further sorption and ethylene hydrogenation studies, which suggested that, the interaction between hydrogen and Pd depended on the environment. Within the electrochemical environment, the ECSA measured, suggested that hydrogen was being reversibly absorbed into the sub-surface octahedral sites of Pd. The higher ECSA for Pd cubes corroborated with higher sorption for Pd cubes as well. However ethylene hydrogenation showed that the fringes of the Pd dendrites provided additional sites for reaction, which in turn translated to higher conversion. Furthermore, through a Koutecky-Levich analysis, it was found out that the Pd dendrites while exhibiting slightly lower activity, favored the 4-electron oxygen reduction process more than the Pd cubes.
In the last part of this dissertation we explored the electrocatalytic properties of Pd-based bimetallic NPs under different morphologies including nanocages and sub-10nm alloys. With the inclusion of Ag, it was found out, through Koutecky-Levich analysis that the 4-electron process was better observed under alkaline conditions using a 0.1M NaOH(aq) electrolyte solution instead of a 0.1M HClO4 (aq) for acidic media testing. It was found that, for PdAg nanocage morphologies, where the Pd galvanically replaced the Ag to form cages, the four-electron process was suited to thinner Pd shells. Indeed the average electron numbers measured for Ag nanocubes coated with a 6nm shell was in agreement, within reason of literature values for bulk Ag. However, since the binding energy that both metals have for OH is so close, the potential for contributions to the ORR kinetics in alkaline media by Pd is a potential consideration.
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Piet, Marvin. "Synthesis and characterization of cathode catalysts for use in direct methanol fuels cells." Thesis, University of the Western Cape, 2010. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_3065_1307691154.
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<p>In this work a modified polyol method was developed to synthesize in-house catalysts. The method was modified for maximum delivery of product and proved to be quick and efficient as well as cost effective. The series of IH catalysts were characterized using techniques such as UV-vis and FT-IR spectroscopy, TEM, XRD, ICP and CV.</p>
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Kurak, Kiera A. "Selenium and Nitrogen-Doped Graphite Elecetrocatalyst Studies for a Proton Exchange Membrane Fuel Cell." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1298570837.
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Mostafa, Ehab [Verfasser]. "Electrocatalysis and Kinetics of the Direct Alcohol Fuel Cells : DEMS and ac Voltammetry Studies / Ehab Mostafa." Bonn : Universitäts- und Landesbibliothek Bonn, 2013. http://d-nb.info/104486804X/34.
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De, A. L. Viana Hermenegildo. "Characterisation of proton conducting oxide materials for use in reverse water gas shift catalysis and solid oxide fuel cells /." St Andrews, 2008. http://hdl.handle.net/10023/429.
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St, John Samuel. "Hierarchical Electrocatalyst Structure Control to Study Cathodic and Anodic Overpotential in Proton Exchange Membrane Fuel Cells." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384334674.
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Lopes, Pietro Papa. "Aproveitamento de etanol em células a combustível: eletrocatálise da reação de oxidação direta e da oxidação do hidrogênio contaminado por CO obtido por sua reforma." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-04072013-152007/.
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Este trabalho compreende estudos das reações de oxidação de hidrogênio na presença de CO em células unitárias do tipo Membrana Trocadora de Prótons e da reação de oxidação de álcoois em meio alcalino em superfícies monocristalinas. Estes dois temas têm como base a utilização de etanol como vetor energético renovável para o uso em dispositivos eletroquímicos conversores de energia, como as células a combustível. O estudo do efeito de temperatura sobre a tolerância ao CO durante a reação de oxidação de hidrogênio foi abordado sob a perspectiva dos diferentes processos de tolerância que ocorrem em materiais de Pt/C, PtRu/C e PtMo/C. Assim, foram utilizadas as técnicas de Microscopia Eletrônica por Transmissão, Espectroscopia por Dispersão de Energia de Raios X, Espectroscopia Fotoeletrônica por Raios X, Difração de Raios X e Espectroscopia de Absorção de Raios X in situ para a caracterização da composição química, estrutura cristalina e de ocupação eletrônica, ressaltando-se o desenvolvimento de uma célula espectro-eletroquímica com o propósito de obter a informação de XAS em um ambiente real de operação da célula, que permite avaliar o efeito da temperatura e do ambiente químico. Estes resultados foram analisados em conjunto com os perfis de polarização anódica, observando-se que o efeito da temperatura opera de maneira distinta sobre os diferentes processos de tolerância ao CO. Uma análise baseada no mecanismo de reação permitiu estimar os recobrimentos experimentais das espécies de H, CO e OH, essencial para compreender os processos que ocorrem nos ânodos de uma PEMFC alimentada com H2/CO. Por outro lado, os estudos da reação de oxidação de etanol em meio alcalino possibilitaram obter informações fundamentais para o entendimento do mecanismo da reação para este e outros álcoois. Este trabalho compreendeu a avaliação do efeito do cátion alcalino sobre a cinética de reação de oxidação de vários álcoois, em destaque no papel da acidez do álcool em conjunto com a presença de Li no efeito eletrocatalítico. Além de observar o papel da acidez dos álcoois e do solvente para a possível promoção do efeito catalítico decorrente de interações não-covalentes, este estudo possibilitou uma ampla análise baseada nas propriedades moleculares dos diferentes álcoois, calculadas por Teoria do Funcional da Densidade. Desta forma foi possível estabelecer uma correlação entre as propriedades dos orbitais de fronteira com a porção da molécula do álcool que irá reagir primeiro, além da diferença de energia entre o Highest Occupied Molecular Orbital - Lowest Unoccupied Molecular Orbital servir de descritor da reatividade sobre uma dada superfície. Foi identificado o papel da oxofilicidade do metal, verificando-se a existência de uma relação próxima entre a adsorção de OH e a de álcool. Por fim, resultados de caracterização do produto da reação por Espectroscopia no Infravermelho, em conjunto com as informações obtidas dos demais estudos, possibilitou propor um mecanismo da reação de oxidação aplicável a diversos álcoois.<br>This work comprises studies of the hydrogen oxidation reaction in the presence of CO in a Proton Exchange Membrane single-cells and the alcohol oxidation reaction in alkaline media on single crystal surfaces. These two themes are based on the use of ethanol as a renewable energy vector in electrochemical energy conversion devices, like fuel cells. The study of the effect of temperature over the CO tolerance during the hydrogen oxidation reaction was tackled with the perspective of the distinct tolerance processes that take place in Pt/C, PtRu/C and PtMo/C materials. Therefore, techniques such as Transmission Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray Diffraction and in situ X-ray Absorption Spectroscopy were employed to characterize the catalysts chemical composition, crystalline structure and electronic occupancy, highlighting the development of a spectro-electrochemical cell with the purpose of obtaining the XAS information under a real operando fuel cell environment, thus allowing evaluations of the effects of temperature and distinct chemical environments. These results were analyzed along with anode polarization profiles, so to emphasize the distinct way that the temperature affects each CO tolerance process. A reaction mechanism analysis allowed estimating the H, CO and OH surface coverages, which are paramount to best understand the processes that take place in PEMFC anodes fed with H2/CO. On the other hand, the ethanol oxidation studies in alkaline media allowed obtaining fundamental information to understand the ethanol oxidation reaction mechanism. These studies comprised the evaluation of the alkali cation effect over the alcohol oxidation reaction kinetics, bringing to light the role of alcohol acidity together with Li to enhance the catalytic effect. Besides observing the acidity role of both alcohol and solvent towards the catalytic promotion resulting from non-covalent interactions, this study allowed a broader analysis based on the molecular properties of distinct alcohols, as calculated by Density Functional Theory. In this way, it was possible to establish a correlation between frontier orbital properties with the portion of the alcohol molecule reacting first, along with the identification of the Highest Occupied Molecular Orbital - Lowest Unoccupied Molecular Orbital energy difference serving as a reactivity descriptor over a given surface. The role of the metal surface oxophilicity was identified, and this evidenced a close relation between OH and alcohol adsorption properties. At last, results obtained from Infrared Spectroscopy so to identify the oxidation products were combined with the information gained from the other studies allowed to elaborate a mechanism for the alcohol oxidation reaction applicable to several distinct alcohols.
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Carbonio, Emilia Andrea. "Síntese e caracterização de nanopartículas do tipo M-MxSy (M = Pt, Rh) suportadas em carbono para eletrocatálise em reações de células a combustível." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-17042012-115001/.
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As Células a combustível são conversores de energia química em energia elétrica. As Células do tipo PEM que funcionam com metanol como combustível tem uma ampla variedade de aplicações. Os materiais utilizados como eletrocatalisadores nas células são responsáveis por uma grande parte do custo das mesmas. Outros problemas, que provocam diminuição da eficiência da célula, são a cinética lenta da reação de redução de oxigênio (RRO) e o potencialmisto gerado devido ao cruzamento de metanol através da membrana. Neste trabalho apresenta-se um estudo de catalisadores do tipo M-MxSy (M = Pt, Rh) para a RRO em meio ácido, com diferentes relações M:MxSy. Os materiais preparados a partir da modificação do método do ácido fórmico (MAF) com tiouréia (TU) foram caracterizados mediante XRD, XPS e XAS. Foi determinado mediante estas técnicas que os catalisadores consistem numa mistura de fases: Pt ou PtRh, PtS, RhxSy e PtS2. O efeito de um tratamento térmico em H2/Ar foi reduzir completamente o PtS2 e parcialmente o PtS. A fase de RhxSy mostrou ser mais estável nas condições do tratamento. Todos os materiais mostraram ter atividade para a RRO e alta seletividade na presença de metanol. Foi determinado que para que a RRO ocorra via 4 elétrons, deve haver sítios metálicos na superfície das nanopartículas. Determinou-se que os materiais contendo maior quantidade de fase MxSy podem ser ativados mediante tratamento térmico ou eletroquímico, melhorando a atividade catalítica frente a RRO e conservando a seletividade na presença de metanol.<br>Fuel cells are dispositives that convert chemical energy into electricity. The PEM fuel cell types that function with methanol as fuel have a wide variety of applications. The materials used as electrocatalysts in the cells are responsible for the major part of their cost. Other problems, that cause decrease in efficiency of the cell, are the slow kinetics of oxygen reduction reaction (ORR) and the mixed potential generated due to methanol crossover through the membrane. This thesis presents a study of M-MxSy-type catalysts (M = Pt, Rh) for the ORR in acid medium, with different M:MxSy ratios. The materials prepared from the modification of the formic acid method (FAM) with thiourea (TU) were characterized by XRD, XPS and XAS. It was determined by these techniques that the catalysts consist of a mixture of phases: Pt or PtRh, PtS, RhxSy and PtS2. The effect of heat treatment in H2/Ar atmosphere was to reduce PtS2 completely and PtS partially. The RhxSy phase proved to be more stable under the treatment conditions. All materials showed to have activity for the ORR and high selectivity in the presence of methanol. It was determined that for the ORR to occur via four electrons, there must be metallic sites at the surface of the nanoparticles. It was determined that the materials containing higher amount of MxSy phase can be activated by thermal or electrochemical treatment, improving the ORR catalytic activity and retaining the selectivity in the presence of methanol.
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Rocha, Thairo de Araújo. "Catalisadores a base de platina e nióbio para o ânodo da célula a combustível de membrana trocadora de prótons alimentada com alcoóis de baixa massa molecular." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-17042012-164635/.
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Neste trabalho descreve-se o estudo das reações de oxidação eletroquímica de metanol e etanol em catalisadores contendo platina (Pt) e Nióbio (Nb) suportados em carbono de alta área superficial. Os materiais estudados foram PtNb/C, Pt-Nb2O5(amorfo)/C e Pt-Nb2O5(cristalino) /C, utilizando-se como padrão para comparação o catalisador comercial Pt/C E-TEK 20 %. A caracterização física foi realizada com o auxílio das técnicas de Difração de Raios X (DRX), Espectroscopia por Energia Dispersiva de Raios X (EDX) e Espectroscopia de Absorção de Raios X (XAS). A partir dos picos de difração foi possível calcular o tamanho médio de cristalito e o parâmetro de rede das amostras estudadas. Os espectros de XAS na região de XANES sugerem que a Pt suportada sobre os óxidos de nióbio tem uma menor tendência a sofrer perda de densidade eletrônica na banda 5d. O comportamento eletroquímico dos catalisadores frente às reações de eletro-oxidação dos alcoóis foi avaliado através de voltametrias de varredura linear, voltametrias cíclicas e cronoamperometrias com o eletrodo de trabalho preparado com uma configuração de camada ultrafina. Os dois catalisadores contendo Pt suportada sobre os óxidos de nióbio apresentaram os melhores desempenhos na oxidação eletroquímica dos alcoóis, no entanto os três materiais estudados deslocaram o pico de oxidação de CO (ads) para menores valores de potencial em relação à Pt/C E-TEK 20 %. Experimentos de Espectroscopia de absorção na região do Infravermelho in situ com Transformada de Fourier (FTIR) foram realizados com o intuito de se identificar os adsorbatos formados durante a eletro-oxidação de etanol. A presença dos óxidos de nióbio não favorece significativamente à conversão de etanol a CO2, sendo os principais produtos da oxidação o acetaldeído e o ácido acético. Por fim foram realizados testes na célula a combustível unitária seguindo-se a mesma abordagem que nos estudos de camada ultrafina.<br>In this work, the methanol and ethanol electrochemical oxidation reactions are studied on platinum (Pt) and niobium (Nb) catalysts supported on high surface area carbon. The selected materials were PtNb/C, Pt-Nb2O5(amorphous) /C e Pt-Nb2O5(crystalline) /C, using as reference for comparison purposes the commercial catalyst 20% Pt-C E-TEK. The catalysts were physically characterized by X-Ray Diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS) and X-ray Absorption Spectroscopy (XAS). The average crystal size and lattice parameters of the studied materials were assessed from the diffraction peaks. XAS spectra in the XANES region indicated that the supported platinum on the niobium oxide possesses a lower tendency to lose electronic density from the 5d band. The electrochemical performance of the different catalysts was evaluated by linear sweep voltammetry, cyclic voltammetry and chronoamperometry, using an ultra-thin layer electrode. The two catalysts containing platinum supported on the niobium oxide showed the best performances for the electrochemical oxidation of the alcohols, though the three studied materials displaced the CO (ads) oxidation peak for lower potential values compared to 20% E-TEK Pt/C. In situ Fourier Transform Infrared Absorption Spectroscopy (FTIR) experiments were carried out in order to identify the formed adsorbates during the ethanol electroxidation. The presence of the niobium oxides does not significantly favour the conversion of ethanol to CO2, being the main products of the oxidation acetaldehyde and acetic acid. Finally, fuel cell tests were carried out following the same procedure as in the case of the ultra-thin layer.
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Zhang, Jingxin. "Investigation of CO tolerance in proton exchange membrane fuel cells." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0708104-193007/.
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Mkhohlakali, Andile Cyril. "Development of nanostructured electrocatalysts using electrochemical atomic layer deposition technique for the direct liquid fuel cells By." University of Western Cape, 2020. http://hdl.handle.net/11394/7346.
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Philosophiae Doctor - PhD<br>The depletion of fossil fuel resources such as coal and the concern of climatic change arising from the emission of greenhouse gases (GHG) and global warming [1] lead to the identification of the 'hydrogen economy' as one of the renewable energy sources and possible futuristic energy conversion solution. Sources of hydrogen as fuel such as water through electrolysis and liquid organic fuel (Hydrogen carriers) have been found as potential game-changers and received increased attention, due to its low-carbon emission.
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Lima, Fabio Henrique Barros de. "\"Desenvolvimento de eletrocatalisadores dispersos para o cátodo de células a combustível alcalinas\"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-11042007-143819/.
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A cinética da reação de redução de oxigênio (RRO) foi estudada em eletrólito alcalino em diferentes eletrocatalisadores. As atividades eletrocatalíticas medidas experimentalmente em metais puros foram correlacionadas com propriedades eletrônicas do eletrocatalisador, como o centro em energia da banda d (εd). A RRO também foi investigada em Pt e Ag modificados pela formação de liga com outros metais de transição. Por fim, a RRO foi conduzida em diferentes óxidos de manganês sintetizados em laboratório, com o objetivo de se determinar a fase mais ativa e o mecanismo da reação nos diferentes óxidos. A atividade eletrocatalítica frente à RRO dos metais puros ou das monocamadas de platina suportadas em diferentes substratos metálicos monocristalinos apresentou uma dependência tipo vulcão em função da energia do centro da banda d do metal eletrocatalisador. Estes resultados indicam que tanto a quebra da ligação O-O como a hidrogenação dos intermediários reacionais têm que ser facilitados, de forma que a cinética das duas reações, as quais são aceleradas por propriedades antagônicas, seja otimizada. O ganho de atividade para a RRO observado para as ligas de Pt em relação à Pt pura foi associado à menor reatividade da Pt na ligas, o que leva à uma menor força da adsorção Pt-O- e, consequentemente, maior cinética de eletroredução dos intermediários oxigenados. A maior atividade das ligas de Ag comparada com a Ag pura foi atribuída à uma mais forte adsorção Ag-O-, o que resulta em maior cinética da quebra da ligação O-O. Os resultados para os diferentes óxidos de Mn mostraram que a ativação para a RRO é maior para os materiais com alto conteúdo de MnO2. A atividade eletrocatalítica dos óxidos de manganês foi associada com um mecanismo acoplado envolvendo uma mudança do estado de oxidação de Mn (IV) para Mn (III), com a transferência de elétrons do Mn (III) para o O2 adsorvido [], em processo via 2 elétrons, com subsequente reação de desproporcionamente do intermediário HO2-, recirculando O2 no sistema, tendendo à um mecanísmo global via 4 elétrons por molécula de O2.<br>The oxygen reduction reaction (ORR) was studied on electrodes formed by Pt monolayers deposited on different metallic substrates, and on carbon-supported electrocatalysts composed by PtM/C (M = V, Cr e Co) and AgPt/C alloys, and on different Mn oxides (Mn3O4/C, Mn2O3/C and MnO2/C) in alkaline electrolyte. The experimentally measured electrocatalytic activities of the different metal catalysts and of the Pt monolayers were plotted against the metal d-band center values (_d). In all cases, the electronic features of the metal electrocatalysts were used for understanding the catalytic activities, and trying to establish the electronic/ORR kinetics relationship. The XANES results for the PtM/C alloys at high electrode potentials have shown lower vacancy of the Pt 5d band compared to pure Pt/C, indicating lower Pt reactivity for adsorbates. The enhanced catalytic activity of Pt in the alloys was attributed to a faster electroreduction of oxygenated intermediates. For the AgPt/C alloys, the XANES results have shown a emptying of the Ag orbitals due to a charge transfer to Pt, and the increased activity of the Ag atoms was ascribed to an electronic effect induced by the presence of Pt, increasing the Ag-O adsorption strength For the manganese oxide materials, the XANES results indicated a chance of the Mn oxidation state as a function of the electrode potential, and higher electrocatalytic activity was observed for MnO2/C. This was explained based on the activation for the ORR, which is higher for the material with higher MnO2 contents and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen.
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Rêgo, Ulisses Alves do. "Redução do Oxigênio Molecular por [Fe(Bipy)3]/C: influência do suporte e do tratamento térmico na atividade catalítica." Universidade Federal do Maranhão, 2011. http://tedebc.ufma.br:8080/jspui/handle/tede/1560.
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Previous issue date: 2011-01-25<br>Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ)<br>This work consisted in the preparation and study of catalytic activity for reduction of molecular oxygen (ROM) based on head-treated coordination compounds with nitrogenated ligands, impregnated on carbon nanosupports (nanotube - NTC, and nanoparticles - Vulcan). The following ions complexes [Fe(bipy)3]2+ and [Fe(TPTZ)2]2+ (2,2 '-bipyridine and 2 ,4,6-tris (2-pyridyl) -1,3,5-triazine) were synthesized and characterized in solution (electron spectroscopy in the region UV-vis, cyclic voltammetry). The following materials were prepared C1: Fe(10%)-Bipy/NTC; C2: Fe(5%) -Bipy/NTC; C3: Fe(5%)-Bipy/Vulcan and C4: Fe(5%)-TPTZ/Vulcan. The comparison between C1 and C2, and between C2 and C3 materials, showed, respectively, the effect of metal loading and the nature of the carbon support on their catalytic efficiency. The comparison among all and C4 (already reported in the literature) allowed the verification of experimental methodology employed. The effect of temperature on the electrocatalytic performance was observed for C1. The following pyrolysis temperatures were used: 600-1000 oC. The results showed that metal loading and the nature of the support influence the catalytic ability of the materials. The best pyrolysis temperature observed to generate active sites in C1 for the ROM was at 800 oC. All materials were treated at this temperature, and the efficiency order observed was: C4 (Fe (5%) -TPTZ/Vulcan) >> C1 (Fe(10%)-Bipy/NTC) > C2 (Fe(5%)-Bipy/NTC) > C3 (Fe (5%) -Bipy/Vulcan). For not heat treated materials, the activity order observed was: C3 (Fe(5%)-Bipy/Vulcan) C4 (Fe (5%)-TPTZ/Vulcan) > C1 (Fe (10%)-bipy/NTC) > C2 (Fe (5%) -Bipy/NTC). C2 and C3 catalysts showed a tendency to reduce the molecular oxygen according to 2e- mechanism, while C1 and C4 materials by 4e- mechanism. For some reason, the TPTZ ligand favored the generation of catalytic sites more efficient than Bipy in these materials.<br>Este trabalho consistiu na preparação e estudos de atividade de catalisadores para redução do oxigênio molecular (ROM) à base de compostos de coordenação com ligantes nitrogenados, impregnados em nanosuportes de carbono e tratados termicamente (nanotubos – NTC; e nanopartículas – Vulcan). Os íons complexos sintetizados e caracterizados em solução por espectrofotometria eletrônica na região Uv-vis, voltametria cíclica, foram: [Fe(Bipy)3]2+ e [Fe(TPTZ)2]2+ (2,2’-bipiridina e 2,4,6-tris(2-piridil)-1,3,5-triazina). Os seguintes materiais foram preparados C1: Fe(10%)-Bipy/NTC; C2: Fe(5%)-Bipy/NTC; C3: Fe(5%)-Bipy/Vulcan e C4: Fe(5%)-TPTZ/Vulcan. A comparação entre os materiais C1 e C2, e entre C2 e C3 permitiu verificar, respectivamente, o efeito da carga do metal e da natureza do suporte de carbono na eficiência catalítica dos materiais. A comparação de todos com o C4 (já relatado na literatura) permitiu a verificação da metodologia experimental empregada. O efeito da temperatura na eficiência eletrocatalítica foi verificado para o C1, empregando-se as temperaturas de pirólise de 600 – 1000 oC. Os resultados mostraram que o suporte e a concentração do metal influenciam na capacidade catalítica dos materiais. A melhor temperatura de pirólise do C1 para a geração de sítios ativos para a ROM foi 800 oC. Os demais materiais foram tratados a esta temperatura, e a ordem de eficiência observada foi: C4 (Fe(5%)-TPTZ/Vulcan) >> C1 (Fe(10%)-Bipy/NTC) > C2 (Fe(5%)-Bipy/NTC) > C3 (Fe(5%)-Bipy/Vulcan). Para os materiais não tratados termicamente, a ordem de atividade observada foi: C3 (Fe(5%)-Bipy/Vulcan) C4 (Fe(5%)-TPTZ/Vulcan) > C1 (Fe(10%)- Bipy/NTC) > C2 (Fe(5%)-Bipy/NTC). Os catalisadores C2 e C3 apresentaram uma tendência em reduzir o oxigênio via um mecanismo de 2e-, enquanto os materiais C1 e C4 por mecanismo de 4e-. O ligante TPTZ, de algum modo, favoreceu mais a geração de sítios catalíticos eficientes nestes materiais que a Bipy.
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Schwämmlein, Jan Nicolas [Verfasser], Hubert A. [Akademischer Betreuer] Gasteiger, Matthias [Gutachter] Arenz, Kai-Olaf M. [Gutachter] Hinrichsen, and Hubert A. [Gutachter] Gasteiger. "Performance and Durability of Ion Exchange Membrane Fuel Cells – From Electrocatalysis to Single Cells / Jan Nicolas Schwämmlein ; Gutachter: Matthias Arenz, Kai-Olaf M. Hinrichsen, Hubert A. Gasteiger ; Betreuer: Hubert A. Gasteiger." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1222161672/34.
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Zhu, Chengzhou, Dan Wen, Martin Oschatz, et al. "Kinetically controlled synthesis of PdNi bimetallic porous nanostructures with enhanced electrocatalytic activity." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-208520.
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Klinsrisuk, Sujitra. "Novel electrocatalytic membrane for ammonia synthesis." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1294.
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Novel ceramic membrane cells of BaCe₀.₅Zr₀.₃Y₀.₁₆Zn₀.₀₄O[subscript(3-δ)] (BCZYZ), a proton-conducting oxide, have been developed for electrocatalytic ammonia synthesis. Unlike the industrial Haber-Bosch process, in this work an attempt to synthesise ammonia at atmospheric pressure has been made. The membrane cell fabricated by tape casting and solution impregnation comprises of a 200 μm-thick BCZYZ electrolyte and impregnated electrode composites. Electrocatalysts for anode and cathode were investigated. For the anode, the co-impregnation of Ni and CeO₂ provided excellent electrode performance including high catalytic activity, sintering stability and compatibility with the BCZYZ electrolyte. The best composition was the mixture of 25 wt% NiO and 10 wt% CeO₂. A symmetrical cell prepared with this electrode composition revealed low polarisation resistances of 1.0 and 0.45 Ωcm² in humidified 5% H₂/Ar at 400 and 500 °C, respectively. For the cathode, 25 wt% of impregnated Fe oxide provided a satisfactory performance in non-humidified N₂ atmosphere. Significant amounts of ammonia were produced from the single cell with Ni-CeO₂ anode and Fe oxide cathode at 400-500 °C under atmospheric pressure. Ammonia formation rate was enhanced by Pd catalyst addition and electrochemical performance was improved by Ru addition. The highest ammonia formation rate of 4 x 10⁻⁹ mols⁻¹cm⁻² was attained using the cell with a Pd-modified Fe cathode at 450 °C. The formation reaction of ammonia typically consumed around 1-2.5 % of total applied current while most of the applied current was employed in H⁺ reduction. The total current efficiency of around 90-100 % could be obtained from the membrane cells.
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De, A. L. Viana Hermenegildo. "Characterisation of proton conducting oxide materials for use in reverse water gas shift catalysis and solid oxide fuel cells." Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/429.
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This study concerned the preparation, characterisation and evaluation of different proton conductors for the Reverse Water Gas Shift Reaction (RWGS) and their evaluation as electrolytes for Solid Oxide Fuel Cells (SOFC) under H₂ and O₂. Materials with both catalytic and conductive properties are of a great interest, as their use in electrocatalytical systems may be very important. Sr₃CaZr₀.₅Ta₁.₅O₈.₇₅ (SCZT), BaCe₀.₉Y₀.₁O₂.₉₅ (BCY10) and Ba₃Ca₁.₁₈Nb₁.₈₂O₈.₇₃ (BCN18), were the initial materials in this study. Thermogravimetric analysis under different atmospheres (5%H₂/Ar, Ar, 5%CO₂, etc), were performed on SCZT and BCN18; with both materials being shown to be stable under reducing and oxidising conditions. Conductivity measurements by two terminal a.c. impedance were also conducted on SCZT and BCN18 under oxidising and reducing atmospheres. As found in literature, BCN18 showed mixed conductivity; with electronic conductivity at high temperatures and pure ionic conductivity below 550ºC, This behaviour was shown in chapter 3, where the change on conduction process was observed upon different gas feeds. Its maximum conductivity values for the different atmospheres were: 8.50x10⁻⁵ S/cm (Dry 5%H₂/Ar at 200ºC), 4.24x10⁻⁴ S/cm (Wet 5%H₂/Ar at 500ºC) and 4.48x10⁻³ S/cm (Air at 900ºC). SCZT proton conducting behaviour was also measured (wet and dry 5%H₂/Ar). Exhibiting an order of magnitude higher in total conductivity upon hydration of the gas feed (σdry=1.01x10⁻⁶ and σwet=1.07x10⁻⁵ at 450ºC). The doping of barium cerate with Zr and Zn by Tao and Irvine, lead to a more stable and easily sinterable BaCe₀.₅Zr₀.₃Y₀.₁₆Zn₀.₀₄O₃ (BCZYZ). Following this work, the introduction of ZnO as a sintering aid to SCZT and BCN18 resulted in Sr₃CaZr₀.₄Ta₁.₅Zn₀.₁O₈.₇₅ (SCZTZ), and Ba₃(Ca₁.₁₈Nb₁.₇₀Zn₀.₁₂)O₈.₅₅ (BCNZ); with higher final densities (above 90% dense). As with BCN18, BCNZ also exhibited mixed conductivity; with higher total conductivity values than BCN18. A maximum of total conductivity of 1.85x10⁻³ S/cm at 900ºC for BCNZ was measured against 6.99x10⁻⁴ S/cm at 900ºC for BCN18. A change in conductivity process was observed when using air or wet 5%H₂/Ar, achieving a maximum of 3.85x10⁻⁴ S/cm at 400ºC when under wet hydrogen. All materials (as powders) have shown catalytic activity for the reverse water gas shift (RWGS) reaction, with the lowest conversion temperature onset at 400ºC for SCZT and a maximum conversion of CO₂ to CO of 42%, with circa 0.52 and 0.59 mmol/s.m² of CO produced at 900ºC by BCN18 and BCZYZ, respectively. No relation between mechanisms for the RWGS and σ for these materials were expected below 10% conversion, as no correlation was found between their activation energies. BCY10 as shown a partial decomposition when exposed to the RWGS reaction, for what BCZYZ After fuel cell testing under H₂ and O₂ both SCZTZ and BCNZ showed mixed conductivity. SCZTZ under different hydrogen partial pressures, exhibited a behaviour close to a pure proton conductor, however, when exposed to both reducing and oxidising conditions, its behaviour did not follow the theoretical values. On the other hand, BCNZ behaves as a pure ionic conductor below 500ºC; with increasing influence of the electronic conductivity on temperature increase. However, as seen for BCNZ conductivity data from 2 terminal a.c. impedance, below 650ºC wet 5%H₂ exhibited the highest conductivity values. This, in additions to the pure ionic conductive behaviour below 400ºC (from the effective ionic transport number), suggests that BCNZ becomes closer to a pure proton conductor with temperature decrease.
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Gonçalves, Bruna Rodrigues Lopes [UNESP]. "Estudo da eletrocatálise da reação de oxidação do glicerol sobre as fases intermetálicas ordenadas PtSn e AuSn." Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/88457.
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goncalves_brl_me_bauru.pdf: 1866198 bytes, checksum: 6cb837c9d2ac03ec4728070b23227b74 (MD5)<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>Atualmente, as mudanças climáticas e a questão energética tem sido tema de grande interesse e discussões mundiais. Assim, um número crescente de novas tecnologias verdes tem sido propostas para transformar o modo como a energia é produzida, distribuída e consumida. Neste contexto, as células a combustível surgem como sistemas alternativos para a geração de energia elétrica. Porém, alguns desafios ainda precisam ser vencidos para sua utilização. Um dos principais desafios refere-se ao desenvolvimento de eletrocatalisadores que favoreçam a oxidação direta do combustível a 'CO IND. 2' e que sejam menos susceptíveis ao envenenamento por intermediários/produtos provenientes desta reação. Neste contexto, as fases intermetálicas ordenadas tem sido propostas como promissores materiais para aplicações em eletrocatálise, pois apresentam estabilidade físico-química, excelente capacidade de adsorção de combustíveis orgânicos e menor susceptibilidade ao bloqueio por intermediários e produtos de reação. O presente trabalho propõe o uso das fases intermetálicas ordenadas PtSn e AuSn como materiais eletrocatalisadores para a reação de oxidação do glicerol, em meio ácido e alcalino. As fases intermetálicas ordenadas foram sintetizadas a partir da fusão dos metais puros em um forno a arco voltaico, sob atmosfera de argônio, e posteriormente refundidos em um forno de indução térmica. Os materiais obtidos foram caracterizados fisicamente pelas técncas de Difração de Raios-X (DRX) e Microscopia Eletrônica de Varredura com Energia Dispersiva de Raios-X (MEV-EDX), cujos resultados mostraram que a metodologia utilizada levou a obtenção dos materiais desejados. A avaliação da atividade eletrocatalítica das fases intermetálicas PtSn e AuSn frente a reação de oxidação do glicerol em eletrólito de 'H IND...<br>Currently, the climatic changes and the energy question have been subject of great interest and world-wide discussions. Thus, an increasing number of new green technologies has been proposed to transform the way as the energy is produced, distributed and consumed. In this context, the fuel cells appear as alternative systems for electric energy generation. One of the main challenges is in the eletrocatalysts development that favor the direct oxidation of 'CO IND. 2' fuel and that products proceeding from this reaction are less likely to the poisoning for intermediate products from this reaction. In this context, the ordered intermetallic phases have been proposed as promising materials for applications in electrocatalysis, therefore they present physicochemical stability, excellent organic fuels adsorption capacity and minor susceptibility to intermediate blocking and reaction products. In this direction, the present work considers the use of PtSn and AuSn ordered intermetallic phases as electrocatalysts material for glycerol oxidation reaction, in acid and alkaline medium. The ordered intermetallic phases have been synthecized from pure metals fusing in an electric-arc furnace, under argon atmosphere, and later melted in an induction furnace. The gotten materials have been physically characterized by X-Ray Diffraction (DRX) and Scanning Electron Microscopy with surface analysis by Energy Dispersive X-ray Spectrometry (MEV-EDX) techniques, which results have shown that the used methodology led to obtaining the desired materials. The electrocatalytic activity evaluation of the PtSn and AuSn intermetallic phases facing the reaction of glycerol oxidation in electrolyte 0,15 'H IND. 2''SO IND. 4' mol 'L POT. -1' and 0,15 NaOH mol 'L POT. -1' and 0,15 NaOh mol 'L POT. -1', was made using the cyclic voltammetry and cronoamperometry techniques. Through these assays, a catalytic... (Complete abstract click electronic access below)
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Silva, Gabriel Christiano da. "Estudo do desempenho e estabilidade de catalisadores Pt-Y/C em cátodo de célula a combustível." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-06052015-110905/.
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Os problemas ambientais originados pela produção e consumo das tradicionais fontes de energia pressionam a sociedade pelo desenvolvimento e utilização de fontes de energia limpas e renováveis. Dentre as novas tecnologias, células a combustível de membrana de troca protônica (PEMFC) apresentam-se como uma alternativa viável, aliando elevadas taxas de conversão energética a níveis mínimos de poluentes gerados. No entanto, a utilização plena desses dispositivos depende de fatores como desempenho, estabilidade e custo dos mesmos. Um dos principais elementos que afeta o desempenho de uma PEMFC é a eficiência com o qual o oxigênio é reduzido no cátodo. Assim, diversos estudos visando a obtenção de eletrocatalisadores à base de Pt que apresentem bom desempenho frente à reação de redução de oxigênio (RRO) e elevada estabilidade têm sido desenvolvidos, recebendo destaque os catalisadores Pt-Y. Neste trabalho catalisadores Pt-Y, com diferentes proporções entre os metais, suportados em carbono de alta área superficial foram sintetizados através de uma modificação no método do ácido fórmico. Os materiais foram caracterizados através das técnicas de EDX, XRD, TEM e XPS, e avaliados frente à RRO através de medidas em meia célula, empregando-se a técnica de eletrodo de disco rotatório, e em célula unitária, como cátodo de PEMFC. O catalisador Pt-Y/C 7:3 foi o que apresentou melhor desempenho dentre os materiais bimetálicos. Através dos testes de envelhecimento acelerado (TEA) constatou-se que, além da degradação das nanopartículas de platina, o ítrio passa por dissolução.<br>The environmental impacts generated by the production and consumption of traditional energy sources leads society to develop clean and renewable energy sources. Among the new technology, proton exchange membrane fuel cells (PEMFC) appear as viable alternative, allying high energy conversion rates to minimum levels of pollutants generated. However, the full utilization of these devices depends on factors such as its performance, stability and cost. One of the major elements that affect the PEMFC performance is the cathode performance. Thus, several studies aiming at obtaining Pt based electrocatalysts with good performance for oxygen reduction reaction (ORR) and high stability have been developed, receiving attention the Pt-Y catalysts. In this work Pt-Y catalysts, supported on high surface area carbon, were synthesized through a modification on formic acid method. The materials were characterized using EDX, XDR, TEM and XPS, and evaluated towards ORR through measurements in half cell, using rotating disk electrode technique, and in unit cell, as cathode of PEMFC. The catalyst Pt-Y/C 7:3 had the best performance among the bimetallic materials. Through accelerated aging tests (AGT), in addition to platinum nanoparticles degradation, yttrium dissolution was also observed.
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Jain, Deeksha. "Development of Alternative Materials to Replace Precious Metals in Sustainable Catalytic Technologies." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1566176607919202.
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Bonnin, Egilda Purusha. "Electrolysis of Ammonia Effluents: A Remediation Process with Co-generation of Hydrogen." Ohio : Ohio University, 2006. http://www.ohiolink.edu/etd/view.cgi?ohiou1156435340.
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Martino, Drew J. "Evaluation of Electrochemical Storage Systems for Higher Efficiency and Energy Density." Digital WPI, 2017. https://digitalcommons.wpi.edu/etd-dissertations/470.
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Lack of energy storage is a key issue in the development of renewable energy sources. Most renewables, especially solar and wind, when used alone, cannot sustain a reliably constant power output over an extended period of time. These sources generally generate variable amounts of power intermittently, therefore, an efficient electrical energy storage (EES) method is required to better temporally balance power generation to power consumption. One of the more promising methods of electrical energy storage is the unitized regenerative fuel cell (UFRC.) UFRCs are fuel cells that can operate in a charge-discharge cycle, similar to a battery, to store and then to subsequently release power. Power is stored by means of electrolysis while the products of this electrolysis reaction can be recombined as in a normal fuel cell to release the stored power. A major advantage of UFRCs over batteries is that storage capacity can be decoupled from cell power, thus reducing the potential cost and weight of the cell unit. Here we investigate UFRCs based on hydrogen-halogen systems, specifically hydrogen-bromine, which has potential for improved electrode reaction kinetics and hence cheaper catalysts and higher efficiency and energy density. A mathematical model has been developed to analyze this system and determine cell behavior and cycle efficiency under various conditions. The conventional H2-Br2 URFCs, however also so far have utilized Pt catalysts and Nafion membranes. Consequently, a goal of this work was to explore alternate schemes and materials for the H2-Br2 URFC. Thus, three generations of test cells have been created. The first two cells were designed to use a molten bromide salt, ionic liquid or anion exchange membrane as the ion exchange electrolyte with the liquids supported on a porous membrane. This type of system provides the potential to reduce the amount of precious metal catalyst required, or possibly eliminate it altogether. Each cell showed improvement over the previous generation, although the results are preliminary. The final set of results are promising for anion exchange membranes on a cost basis compared Nafion. Another promising energy storage solution involves liquid methanol as an intermediate or as a hydrogen carrier. An alternative to storing high-pressure hydrogen is to produce it on-board/on-site on demand via a methanol electrocatalytic reformer (eCRef), a PEM electrolyzer in which methanol-water coelectrolysis takes place. Methanol handling, storage, and transportation is much easier than that for hydrogen. The hydrogen produced via methanol eCref may then be used in any number of applications, including for energy storage and generation in a standard H2-O2 PEM fuel cell. The mathematical modeling and analysis for an eCref is very similar to that of the HBr URFC. In this work, a comprehensive model for the coelectrolysis of methanol and water into hydrogen is created and compared with experimental data. The performance of the methanol electrolyzer coupled with a H2-O2 fuel cell is then compared for efficiency to that of a direct methanol fuel cell data and was found to be superior. The results suggest that an efficient and small paired eCRef-fuel cell system is potentially be a cheaper and more viable alternative to the standard direct methanol fuel cell. Both the H2-Br2 URFC and the methanol eCref in combination with a H2-O2 fuel cell have significant potential to provide higher energy efficiency and energy density for EES purposes.
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Jacob, Juliana Marciotto. "Efeito da adição de cério em catalisadores Pt/C e PtSn/C para eletro-oxidação de etanol." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-04072014-121032/.
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Neste trabalho foi estudado o efeito da presença do cério em catalisadores de Pt/C e PtSn/C para eletro-oxidação de etanol visando aumentar a eficiência da reação, entender o motivo das variações na atividade catalítica e avaliar a estabilidade destes catalisadores nas condições de operação da célula. Todos os catalisadores foram preparados pelo método do ácido fórmico, os dados de espectroscopia XPS confirmaram as porcentagens nas composições dos catalisadores de PtCe/C e PtSnCe/C. Através das técnicas de TEM e XRD verificou-se que, com exceção da proporção PtCe/C 50:50, todos os outros catalisadores apresentaram tamanho de partícula próximos ao tamanho de cristalito. Os dados de XRD não indicam a presença de liga nos catalisadores de PtCe/C e de PtSnCe/C, mas mesmo em forma de óxido, o estanho apresentou um efeito eletrônico, como informado pelos dados de XAS. A adição de cério promove a oxidação do etanol em menores potenciais que a platina. A adição de estanho ao catalisador PtCe/C teve um efeito benéfico na atividade catalítica promovendo a oxidação em potenciais inferiores aos catalisadores de PtCe/C. A interação de Pt-Sn promove a dissociação da água para formar Sn-OHad próximo a espécies de monóxido de carbono adsorvidas na Pt, facilitando a rápida oxidação de etanol. Os testes de estabilidade indicaram que ao comparar os catalisadores PtSnCe/C com um catalisador comercial de PtSn/C, é possível aferir que a adição de cério promove uma melhora da estabilidade do catalisador.<br>In this work, the effect of the cerium presence in Pt/C and PtSn/C catalysts for ethanol electro-oxidation was studied to increase the efficiency of the reaction, to understand the variations in catalytic activity and to evaluate the catalysts stability at the cell operating conditions. All catalysts were prepared by the formic acid method, and the XPS data confirmed the percentages in the compositions of the catalyst PtCe/C and PtSnCe/C. The XRD and TEM data showed that, with the exception of the proportion PtCe/C 50:50, all other catalysts showed particle size close to the crystallite size. The XRD data does not indicate the presence of alloy in the PtCe/C and PtSnCe/C catalysts, but even in the form of oxide, tin presented an electronic effect, as reported by the XAS data. The addition of cerium promotes oxidation of ethanol in lower potential than platinum. The addition of tin in this catalyst had a beneficial effect on the catalytic activity, promoting the oxidation in lower potential than the PtCe/C catalysts. The interaction of Pt-Sn promotes the dissociation of water to form Sn-OHad near species of carbon monoxide adsorbed on Pt, facilitating the rapid ethanol oxidation. Stability tests showed when comparing PtSnCe/C catalyst with commercial catalyst PtSn/C, it was possible to determine that the addition of cerium provides an improvement of the catalyst stability.
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Carvalho, Dayvid Pires. "ELETROCATALISADORES À BASE DE Fe,Co(10%m)-N(PAR,PAN)/C(500-900 ºC) PARA A REDUÇÃO DO OXIGÊNIO MOLECULAR." Universidade Federal do Maranhão, 2014. http://tedebc.ufma.br:8080/jspui/handle/tede/991.
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Previous issue date: 2014-08-29<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>In order to develop a new Pt-free reducing agents for oxygen reduction reaction (ORR),
the ligands 1 - (2-Pyridylazo)-2-naphthol (PAN) and 4-(2-pyridylazo)-resorcinol (PAR) were studied as nitrogen sources complexing with Fe (II) and Co (II) ions, supported on carbon nanoparticles (10 wt. % metal loading) and heat treated at temperature of 500, 700 and 900°C. The synthesized complexes ([ML₂]; M²⁺= Fe, Co; L = PAN, PAR) were characterized by UVVis and Infrared spectroscopies before impregnation step. By cyclic voltammetric technique it was found that all eletrocatalysts showed an increase of performance for ORR after heat treated and that the highest efficiency were reached by: Fe-PAN/C -700°C (0,818 V x ENH), Fe-PAN/C- 900 °C (0,786V x ENH), Co-PAN/C - 500 °C (0,657V x ENH) e Co-PAN/C - 700°C (0.673 V x ENH), e Co-PAN/C - 900°C (0.612 V x ENH), Co-PAR/C - 700°C (0.588 V x ENH), Co-PAR/C - 900°C (0.623 V x ENH) e Fe-PAR/C - 700°C (0.598 V x ENH). With EDR studies, it was possible to calculate, with Koutecký Levich equation, the number of electrons involved in the ORR for each catalyst at potentials of 0.1, 0.2, 0.3 and 0.4 V. Except COPAR-700 °C which the adopted method did not allow the the number of electrons, the other catalysts, which were calculated were nearer the behavior of a mechanism via 2 and 4e- while others saw.<br>Com o intuito de desenvolver um novo agente redutor livre de platina para reacção de redução de oxigênio (RRO), os ligantes de 1 - (2-Piridilazo)-2-naftol (PAN) e 4 - (2-piridilazo)- resorcinol (PAR) foram estudados como fontes de nitrogenio complexantes com os íons Fe (II) e Co (II), suportados em nanopartículas de carbono (10% de carga de metais) e tratados termicamente a uma temperatura de 500, 700 e 900 °C. Os complexos sintetizados ([ML₂]; M²⁺ = Fe, Co, L = PAN, PAR) foram caracterizados por UV-Vis e espectroscopia de infravermelho antes da etapa de impregnação. Pela técnica de voltametria cíclica, verificou-se que todos os
catalisadores mostraram um aumento de desempenho para a RRO após o tratamento térmico e
que a maior eficiência foram alcançados por: Fe-PAN/C -700°C (0,818 V x ENH), Fe-PAN/C- 900 °C (0,786V x ENH), Co-PAN/C - 500 °C (0,657V x ENH) e Co-PAN/C - 700°C (0.673 V x ENH), e Co-PAN/C - 900°C (0.612 V x ENH), Co-PAR/C - 700°C (0.588 V x ENH), Co- PAR/C - 900°C (0.623 V x ENH) e Fe-PAR/C - 700°C (0.598 V x ENH). Com os estudos de EDR, foi possível calcular, com a equação de Koutecky-Levich, o número de eletrons
envolvidos na RRO para cada catalisador nos potenciais de 0,1, 0,2, 0,3 e 0,4V. Com exceção do CoPAR-700°C o qual o método adotado não permitiu que fosse calculado o número de elétrons, os demais catalisadores, apresentaram comportamento próximos do mecanismo via
2e- enquanto outros via 4e-.
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Corradini, Patricia Gon. "Efeito da adição de praseodímio em catalisadores de Pt e PtSn/C para eletro-oxidação de etanol." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-20032013-102655/.
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O efeito da presença do praseodímio em catalisadores de Pt/C e PtSn/C para eletro-oxidação de etanol foi estudado neste trabalho. Os principais objetivos foram estudar alterações na rota sintética da metodologia do ácido fórmico, visando catalisadores com propriedades físico-químicas que aumentem a eficiência frente a reação de oxidação de etanol; entender o motivo das variações na atividade catalítica; e avaliar a estabilidade dos catalisadores nas condições de operação da célula. A atmosfera de síntese dos catalisadores de PtPr/C influencia fortemente as atividades catalíticas destes materiais. Os catalisadores sintetizados em atmosfera de CO apresentaram antecipação do potencial de pico de oxidação de CO e maior área ativa em relação aos materiais sintetizados em atmosfera de hidrogênio. A mudança de atmosfera para gás CO promoveu mudanças físicas como a redução do tamanho médio de cristalito e tamanho médio de partícula. A adição de praseodímio promove a oxidação do etanol em menores potenciais que a platina, por favorecer o mecanismo bifuncional. A adição de estanho ao catalisador PtPr/C teve um efeito benéfico na atividade catalítica. Os dados DRX não indicam alto grau de liga Pt-Sn, mas mesmo em forma de óxido, o estanho apresentou um efeito eletrônico, como informado pelos dados de XAS. A interação de Pt-Sn promove a dissociação da água para formar Sn-OHad próximo a espécies de monóxido de carbono adsorvidas na Pt, facilitando a rápida oxidação de etanol. Os testes de estabilidade indicaram que os catalisadores PtSnPr/C apresentam grande variação da área ativa com sucessivas ciclagens. Apesar da dissolução de espécies de estanho, a adição de praseodímio contribuiu para elevar a estabilidade dos catalisadores sintetizados.<br>The effect of praseodymium presence in Pt/C and PtSn/C catalysts for ethanol electro-oxidation was investigated. The main objectives were the evaluation of a modified formic acid synthesis method for the preparation of PtPr/C and PtSnPr/C catalysts with enhanced activity for the ethanol oxidation reaction and stability at the cell operating conditions. The synthesis atmosphere of PtPr/C catalysts highly influences the catalytic activity of these materials. The catalysts synthesized in CO atmosphere showed a lower onset potential for CO oxidation and a higher active surface area than those synthesized in a hydrogen atmosphere. The CO atmosphere promoted physical changes such as reduction of crystallite size and particle size. Addition of praseodymium to Pt/C catalyst improved the activity for ethanol oxidation by the bifunctional mechanism. Tin addition to the PtPr/C catalyst had a beneficial effect on catalytic activity. XRD data no indicated Pt-Sn alloy, but even in oxide form, tin presented an electronic effect, as reported by XAS data. The interaction of Pt with Sn promotes the dissociation of water to form Sn-OHadsorbed close to carbon monoxide adsorbed on the Pt, and it facilitates a fast ethanol oxidation. Stability tests showed a change in the active area of the PtSnPr/C catalysts after repetitive potential cycling. Although the tin species dissolution, the praseodymium addition increased the catalysts stability.
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Guenot, Benoit. "Etude de matériaux catalytiques pour la conversion électrochimique de l'énergie Clean hydrogen generation from the electrocatalytic oxidation of methanol inside a proton exchange membrane electrolysis cell (PEMEC): effect of methanol concentration and working temperature Electrochemical reforming of Dimethoxymethane in a Proton Exchange Membrane Electrolysis Cell: a way to generate clean hydrogen for low temperature fuel cells." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2017. http://www.theses.fr/2017ENCM0004.
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L’hydrogène est un vecteur énergétique prometteur réalisant une très bonne synergie avec l’exploitation des sources d’énergie intermittentes telles que le solaire ou l’éolien. Le développement de ses moyens de production et de conversion électrochimique représente un enjeu majeur dans le contexte de transition énergétique dans lequel nous vivons aujourd’hui. Les piles à combustible et les électrolyseurs utilisant la technologie PEM (Membrane Echangeuse de Protons) sont des systèmes électrochimiques de conversion de l’énergie matures tandis que les systèmes réversibles capables de remplir ces deux fonctions – les piles à combustible régénératrices unitaires – sont encore à l’état de développement. Leur principal verrou technologique est la conception d’une électrode bifonctionnelle à oxygène. Les matériaux catalytiques mis en œuvre dans ces systèmes sont principalement des métaux nobles et il convient d’en réduire autant que possible la charge massique dans les électrodes pour diminuer le coût des systèmes. Trois aspects complémentaires ont été développés lors de ces travaux de thèse. D’une part, des oxydes d’iridium et de ruthénium ont été élaborés par voie hydrothermale afin de catalyser la génération d’oxygène en fonctionnement électrolyseur. D’autre part, des catalyseurs à base de platine supportés sur des matériaux non carbonés, en particulier le nitrure de titane, ont été synthétisés par des voies colloïdales, afin de catalyser la réduction de l’oxygène en fonctionnement pile à combustible. L’association de ces matériaux est une première étape vers la conception d’une électrode bifonctionnelle à oxygène. Le troisième point se concentre sur la production de l’hydrogène et propose une alternative à l’oxydation de l’eau. L’oxydation électrochimique de composés organiques tels que le méthanol ou le diméthoxyméthane à l’aide de catalyseurs à base de platine et de ruthénium métallique permet la production d’hydrogène de grande pureté avec une consommation d’énergie électrique moindre par rapport à l’électrolyse de l’eau<br>Hydrogen is a promising energy vector, particularly for energy storage from intermittent energy sources such as solar or wind. The development of its production methods and its electrochemical conversion represents a major challenge in the context of energy transition in which we live nowadays. Fuel cells and electrolyzers using PEM technology (Proton Exchange Membrane) are mature electrochemical energy conversion systems, while reversible systems capable of performing both functions – unitized regenerative fuel cells – are still in the early stage of development. Their main technological bottleneck is the design of a bifunctional oxygen electrode. The catalytic materials used in these systems are mainly noble metals and it is necessary to reduce as much as possible their loading in the electrodes to decrease the system cost. Three complementary aspects have been developed during this thesis. On the one hand, iridium and ruthenium oxides have been prepared by hydrothermal treatment in order to catalyze the oxygen evolution under electrolyzer operation. On the other hand, platinum-based catalysts supported on non-carbonaceous materials, especially titanium nitride, have been synthesized by colloidal routes, in order to catalyze the oxygen reduction under fuel cell operation. The combination of these materials is the first step towards the design of a bifunctional oxygen electrode. The third topic focuses on the production of hydrogen and proposes an alternative to the oxidation of water. The electrochemical oxidation of organic compounds such as methanol or dimethoxymethane using platinum and ruthenium based catalysts allows producing clean hydrogen with a lower electrical energy consumption compared to the electrolysis of water
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DRESCH, MAURO A. "Aplicação de catalisadores PtSn/C e membranas Nafion-SiOsub(2) em células a combustível de etanol direto em elevadas temperaturas." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10633.
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Made available in DSpace on 2014-10-09T12:42:37Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T14:01:33Z (GMT). No. of bitstreams: 0<br>Tese (Doutorado em Tecnologia Nuclear)<br>IPEN/T<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Lopes, Pietro Papa. "Estudos da reação de oxidação de hidrogênio na presença de CO no sistema eletrocatalítico Pt-Ru/C." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-25082009-105950/.
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Neste trabalho são apresentados resultados de estudos dos efeitos do pH e da atmosfera de síntese de eletrocatalisadores de Pt/C, Ru/C e PtRu/C sobre suas propriedades catalíticas frente à reação de oxidação de hidrogênio (ROH) na presença de CO. Também são comparados os desempenhos destes materiais em configurações eletródicas de misturas físicas de Pt/C + Ru/C, com o intuito de caracterizar o papel de cada catalisador sobre o mecanismo de tolerância ao CO, sobre fenômenos de oscilação do potencial anódico e sobre a produção transiente de metano, particularmente nos materiais de Ru/C. Em conjunto com os resultados experimentais, foram realizadas simulações cinéticas das respostas experimentais de voltametria de stripping de CO e dos experimentos de troca de gás, de forma a entender os processos de oxidação do CO e sua redução a metano, bem como dos efeitos sobre a eletrocatálise da ROH. Pode-se observar claramente elevada tolerância ao CO no sistema eletrocatalítico Pt-Ru/C, destacando-se a maior atividade dos materiais de PtRu/C e Ru/C sintetizados sob atmosfera redutora (H2), assim como a influência dos parâmetros de pH e atmosfera de síntese sobre o desempenho dos materiais de Pt/C. Através dos eletrodos constituídos por misturas físicas de Pt/C + Ru/C, foi possível discutir os efeitos do Ru sobre a atividade catalítica da Pt, verificando-se que a influência do efeito eletrônico é clara sobre os processos de adsorção/dessorção do CO adsorvido na Pt. Os resultados das simulações cinéticas ajudaram a entender os processos de oxidação do CO, identificando-se que em materiais de Pt/C o mecanismo aceito atualmente necessita de revisão em relação às espécies ativas desta reação. As simulações dos experimentos de troca de gás com produção de metano correspondem bem aos resultados experimentais, destacando-se que a influência das variáveis eletroquímicas se dá de forma direta sobre a etapa de hidrogenação do CO.<br>This work shows results of studies regarding the effects of pH and atmosphere of the synthesis on the electrocatalytic properties of Pt/C, Ru/C and PtRu/C materials for the hydrogen oxidation reaction (HOR) in the presence of CO. The performance of these materials were compared for distinct eletrodic configurations of Pt/C + Ru/C physical mixtures, to characterize the role of each catalyst on the CO tolerance mechanisms, the phenomena of anodic potential oscillations, and the transient methane production, particularly for Ru/C. Comparisons of kinetic simulation data with experimental results were carried out for CO stripping voltammetry and gasexchange results, in order to discuss the CO oxidation and reduction processes, as well as the mechanisms of the HOR electrocatalysis. The CO tolerance effects were clearly observed for all Pt/C-Ru/C electrocatalytic systems, with the PtRu/C and Ru/C materials synthesized under reductive atmosphere (H2) showing the highest activity and the performance of the Pt/C materials shows large dependence on the pH and the synthesis atmosphere. For the electrodes with Pt/C + Ru/C physical mixtures the CO tolerance properties was discussed in terms of the effect of Ru on the electronic properties of Pt, which affects the CO adsorption/desorption process in the Pt sites. The results of the kinetic simulations were useful to understand the CO oxidation processes and to show that the accepted mechanism for the Pt/C material needs some revision regarding the nature of the active species participating in the reaction. The results of the simulations of the gas exchange responses for methane production agree well with the experiments, also evidencing that the effects of the electrochemical variables occurs directly over the CO hydrogenation step.
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Hamer, P. "Electrocatalysis towards direct fuel cell applications." Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676493.
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The aim of this thesis is an in depth study of electro-oxidation of ethanol, but also that of alternate fuels to allow a direct comparison under a range of conditions. Polycrystalline metal electrodes are used in a half cell set up as model environment for the electrochemical studies of several catalytic surfaces. Due to the limited research that has been carried out, for the first time chapters 3 and 4 of the thesis provide electrochemical studies into the electro oxidation of ethanol, ethylene glycol, acetaldehyde and acetic acid on polycrystalline rhodium while simultaneously studying temperature, concentration and electrolyte. Chapter 5 investigates the effect of changing platinum coverage on the surface of polycrystalline rhodium on of ethanol electro-oxidation while also changing temperature and concentration. To the best of my knowledge this is an experiment never before carried out and clearly shows the effect of the varying platinum coverage under a range of conditions. Chapters 6&7 investigate electro-oxidation of C2 molecules on polycrystalline platinum again with varying concentration, temperature and electrolyte. Although Chapter 1 shows similar experiments have been carried out before, using the same electrode for all experiments as well as investigating the effect of varying tin coverage on the platinum surface allows for direct comparisons, as well as providing results to compare with the results of the rhodium experiments. Overall, this thesis provides a systematic and comprehensive study into the electrochemical oxidation of ethanol and other C2 molecules using cyclic voltammetry and chrono amperometry techniques to provide activity and stability information to a degree not reported anywhere else.
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Gonçalves, Bruna Rodrigues Lopes. "Estudo da eletrocatálise da reação de oxidação do glicerol sobre as fases intermetálicas ordenadas PtSn e AuSn /." Bauru : [s.n.], 2010. http://hdl.handle.net/11449/88457.
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Orientador: Antonio Carlos Dias Ângelo<br>Banca: Luiz Henrique Dall'Antonia<br>Banca: Joelma Perez<br>O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da Unesp<br>Resumo: Atualmente, as mudanças climáticas e a questão energética tem sido tema de grande interesse e discussões mundiais. Assim, um número crescente de novas tecnologias verdes tem sido propostas para transformar o modo como a energia é produzida, distribuída e consumida. Neste contexto, as células a combustível surgem como sistemas alternativos para a geração de energia elétrica. Porém, alguns desafios ainda precisam ser vencidos para sua utilização. Um dos principais desafios refere-se ao desenvolvimento de eletrocatalisadores que favoreçam a oxidação direta do combustível a 'CO IND. 2' e que sejam menos susceptíveis ao envenenamento por intermediários/produtos provenientes desta reação. Neste contexto, as fases intermetálicas ordenadas tem sido propostas como promissores materiais para aplicações em eletrocatálise, pois apresentam estabilidade físico-química, excelente capacidade de adsorção de combustíveis orgânicos e menor susceptibilidade ao bloqueio por intermediários e produtos de reação. O presente trabalho propõe o uso das fases intermetálicas ordenadas PtSn e AuSn como materiais eletrocatalisadores para a reação de oxidação do glicerol, em meio ácido e alcalino. As fases intermetálicas ordenadas foram sintetizadas a partir da fusão dos metais puros em um forno a arco voltaico, sob atmosfera de argônio, e posteriormente refundidos em um forno de indução térmica. Os materiais obtidos foram caracterizados fisicamente pelas técncas de Difração de Raios-X (DRX) e Microscopia Eletrônica de Varredura com Energia Dispersiva de Raios-X (MEV-EDX), cujos resultados mostraram que a metodologia utilizada levou a obtenção dos materiais desejados. A avaliação da atividade eletrocatalítica das fases intermetálicas PtSn e AuSn frente a reação de oxidação do glicerol em eletrólito de 'H IND... (Resumo completo, clicar acesso eletrônico abaixo)<br>Abstract: Currently, the climatic changes and the energy question have been subject of great interest and world-wide discussions. Thus, an increasing number of new green technologies has been proposed to transform the way as the energy is produced, distributed and consumed. In this context, the fuel cells appear as alternative systems for electric energy generation. One of the main challenges is in the eletrocatalysts development that favor the direct oxidation of 'CO IND. 2' fuel and that products proceeding from this reaction are less likely to the poisoning for intermediate products from this reaction. In this context, the ordered intermetallic phases have been proposed as promising materials for applications in electrocatalysis, therefore they present physicochemical stability, excellent organic fuels adsorption capacity and minor susceptibility to intermediate blocking and reaction products. In this direction, the present work considers the use of PtSn and AuSn ordered intermetallic phases as electrocatalysts material for glycerol oxidation reaction, in acid and alkaline medium. The ordered intermetallic phases have been synthecized from pure metals fusing in an electric-arc furnace, under argon atmosphere, and later melted in an induction furnace. The gotten materials have been physically characterized by X-Ray Diffraction (DRX) and Scanning Electron Microscopy with surface analysis by Energy Dispersive X-ray Spectrometry (MEV-EDX) techniques, which results have shown that the used methodology led to obtaining the desired materials. The electrocatalytic activity evaluation of the PtSn and AuSn intermetallic phases facing the reaction of glycerol oxidation in electrolyte 0,15 'H IND. 2''SO IND. 4' mol 'L POT. -1' and 0,15 NaOH mol 'L POT. -1' and 0,15 NaOh mol 'L POT. -1', was made using the cyclic voltammetry and cronoamperometry techniques. Through these assays, a catalytic... (Complete abstract click electronic access below)<br>Mestre
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Gentil, Tuani Carla. "Estudo da adição de nanobarras de CeO2 em eletrocatalisadores híbridos à base de PtSn para oxidação eletroquímica de etanol em meio ácido." reponame:Repositório Institucional da UFABC, 2018.
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Orientador: Prof. Dr. Mauro Coelho dos Santos<br>Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência e Tecnologia/Química, 2018.<br>Eletrocatalisadores Pt/C e PtSn/C (20% em massa de metal no suporte) foram sintetizados pelo método de Redução Química por Borohidreto de Sódio, sendo adicionadas nanobarras (nanorods-NR) de CeO2 aos materiais binários, nas porcentagens de 5, 10 e 20% da carga metálica, para a formação do material híbrido. As razões mássicas obtidas por meio dos experimentos de MEV-EDS para Pt3Sn1/C (75:25), Pt2Sn1/C (67:33), Pt1Sn1/C (50:50) e Pt3Sn1_%NR/C (75:25) encontraram-se próximas às composições nominais de partida. O tamanho médio de cristalito variou de 1 a 4 nm para os materiais sintetizados. Por meio dos difratogramas de raios X verificou-se que não houve formação de liga entre platina (Pt) e estanho (Sn) a partir dos cálculos de parâmetro de rede para os picos (111); (200) e (220) da platina, e observou-se a distribuição das nanopartículas no suporte de forma mais aglomerada para os materiais contendo Sn e NR, por meio da Microscopia Eletrônica de Transmissão (MET). Os experimentos eletroquímicos revelaram que os eletrocatalisadores Pt/C e PtSn/C apresentaram picos bem definidos na região de dessorção/ adsorção de hidrogênio e verificou-se que o eletrocatalisador Pt3Sn1_20%NRCeO2/C se destacou nos experimentos de Stripping de CO por apresentar menor potencial de início de oxidação e maior valor de área superficial eletroquimicamente ativa. Os demais experimentos eletroquímicos para oxidação de etanol mostraram atividade semelhante entre os eletrocatalisadores Pt3Sn1/C e Pt3Sn1_20%NRCeO2/C, tanto em termos de potencial de início de oxidação, verificados por voltametria cíclica, quanto em termos de intensidade de corrente por meio de cronoamperometrias. Experimentos em célula a combustível unitária exibiram maiores valores de potencial de circuito aberto, para o material Pt3Sn1_20%NRCeO2/C, além da promissora atividade quando comparado ao material Pt3Sn1/C em termos de densidade de potência, uma vez que, foram obtidos 3,01 mW cm-2 utilizando-se o eletrocatalisador com NR, para oxidação de etanol, valor este que apresenta-se próximo a 3,82 mW cm-2 obtido com o material Pt3Sn1/C, e superior ao eletrocatalisador Pt/C, que apresentou densidade de potência de 0,62 mW cm-2 nas mesmas condições experimentais.<br>Pt/ C and PtSn/ C electrocatalysts (20% by weight of metal in the support) were synthesized by the Sodium Borohydride Chemical Reduction method, with CeO2 nanorods (NR) added to the binary materials at the percentages of 5, 10 and 20% of the metallic charge, for the formation of the hybrid material. The weight ratios obtained by the SEM-EDS experiments for Pt3Sn1/ C (75:25), Pt2Sn1/ C (67:33), Pt1Sn1/ C (50:50) and Pt3Sn1_% NR/ C (75:25) found close to the nominal starting compositions. The average crystallite size ranged from 1 to 4 nm for the synthesized materials. By means of the X-ray diffractograms it was verified that there was no alloying between platinum (Pt) and tin (Sn) from the network parameter calculations for the peaks (111); (200) and (220) of the platinum, and the distribution of the nanoparticles in the support in a more agglomerated form was observed for the materials containing Sn and NR, by Transmission Electron Microscopy (TEM). Electrochemical experiments showed that the Pt/ C and PtSn/ C electrocatalysts had well defined peaks in the region of hydrogen desorption / adsorption and it was verified that the electrocatalyst Pt3Sn1_20% NRCeO2/ C was highlighted in the CO Stripping experiments because of the lower potential of oxidation onset and higher value of electrochemically active surface area. The other electrochemical experiments for the oxidation of ethanol showed similar activity between the Pt3Sn1/ C and Pt3Sn1_20% NRCeO2/ C electrocatalysts both in terms of oxidation initiation potential, verified by cyclic voltammetry, and in terms of current intensity by means of chronoamperometries. Experiments in the unitary fuel cell exhibited higher open circuit potential values for the Pt3Sn1_20% NRCeO2/ C material, as well as the promising activity when compared to the Pt3Sn1/ C material in terms of power density, since 3.01 mW cm-2 using the electrocatalyst with NR, for the oxidation of ethanol, which is close to 3.82 mW cm-2 obtained with the Pt3Sn1/ C material, and higher than the Pt/ C electrocatalyst. showed a power density of 0.62 mW cm-2 under the same experimental conditions.
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