As computational methods for the prediction of metallic nanoparticle structure and reactivity continue to advance, a need has developed for simple experimental models that can mimic and confirm theoretical predictions. Dendrimer-encapsulated nanoparticles, or DENs, are ideal to fill this role. DENs are synthesized within poly(amido amine) dendrimer templates which allows for the controlled synthesis of monodisperse nanoparticles in the 50-250 atom (1-2 nm) size range. These are small enough to be accessible to high-level theoretical calculations while being large enough to study experimentally. The research reported here consists of several independent but closely related studies. First, the synthesis, structural, and electrochemical properties of Au@Pt (core@shell) DENs are described. These materials are prepared by underpotentially depositing Cu onto Au DENs followed by galvanic exchange of Cu for Pt. Second, Pb UPD onto Au DENs and a detailed experimental and theoretical study of the resulting core@shell particle structures and catalytic activity is discussed. It is found that no matter how much Pt is deposited onto the surface of Au₁₄₇ DENs, a surface reorganization occurs resulting in similar electrocatalytic activity for the oxygen reduction reaction. Third, an in-depth X-ray absorption spectroscopy study of the structural properties of thiol-capped Au₁₄₇ DENs is described. Here, the surfaces of uncapped Au₁₄₇ nanoparticles are titrated with strongly binding thiol ligands to tune the extent of surface disorder. The effect of the increased surface disorder on the standard EXAFS fitting results is discussed from experimental and theoretical perspectives. Lastly, an in-situ electrochemical study of Au₁₄₇ DENs structure is reported. The key result is that the Au lattice expands during electrochemical surface oxidation. This is an important result for understanding electrocatalytic processes on Au nanoparticle / text

<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>

This work focuses on tracking formic acid adsorption as formate onto polycrystalline gold and its subsequent catalyzed oxidation to carbon dioxide. Formic acid oxidation is notoriously dependent on supporting electrolyte composition, a dependency that is little characterized. Additionally, the mechanism of oxidation is in disagreement in the literature. As such, the two preceding topics are the primary focus of this work, and are studied in HClO4 and H2SO4 solutions. Cyclic voltammetry experiments supplemented by mathematical modelling and fitting of data were used. Solution pH and adsorption of supporting electrolyte anions onto Au(poly) were very influential factors in determining formate coverages on Au(poly). This alone explains the effect of supporting electrolyte on this reaction. The coverage of adsorbed formate was found to be singularly responsible for determining the rate of formic acid oxidation. This implies a chemical rate limiting step for oxidation, leaving the oxidation rate constant independent of potential. Another segment of this work focuses on the statistical mechanics of lattice gases, namely the role of sites available for adsorption on the activity. This topic is central to the modelling of multiple adsorbing species in competition for the same adsorption sites. Activity for interaction-free lattice gases in the thermodynamic limit was found to be coverage of adsorbates over coverage of sites available for adsorption. This relationship was exploited to simulate coadsorption of two species, the first obeying the Langmuir isotherm and the second following the hard hexagon isotherm. This system was originally considered as a possible model for coadsorption of formate and sulfate in H2SO4 solutions, but did not match with data. / Graduate / 0494 / jstrobl@uvic.ca

This thesis discusses results on the development of three-dimensional (3D) Ni-based electrocatalytic layers for hydrogen production by water electrolysis in an acidic medium. This is of relevance to the development of polymer-electrolyte-membrane (PEM) hydrogen generators, which are promising hydrogen production systems suitable for both residential and industrial applications. / It was demonstrated that patterning of a glassy carbon electrode substrate with a 3D polyaniline (PANI) matrix is a convenient way of increasing the electrocatalytically active surface area of electrodeposited Ni, and hence its apparent electrocatalytic activity. The optimized PANI/Ni electrocatalyst layer showed a significantly higher activity in the hydrogen evolution reaction (HER) then a commercially available Ni-plate surface (control surface). / It was also demonstrated that it is possible to produce a Ni-based HER electrocatalyst layer by synthesizing Ni nanoparticles and supporting them on Vulcan carbon. This electrocatalyst also offered a significantly higher electrocatalytic activity in the HER then the control surface, but lower then the optimized PANI/Ni electrocatalyst. / The electrocatalytic activity of the optimized PANI/Ni layer was also compared to the activity of a 3D catalyst produced by electro-coating a porous reticulated vitreous carbon (RVC) substrate with Ni. This electrocatalyst showed the highest HER electrocatalytic activity among the investigated layers when tested under potentiodynamic polarization conditions. However, under the potentiostatic conditions, the optimized PANI/Ni layer showed the highest electrocatalytic activity. / The mechanisms and kinetics of the HER on the produced electrocatalysts was also investigated, as well as the electrocatalyst layers' surface morphology and crystalline structure.

Philosophiae Doctor - PhD / South Africa is undergoing a serious consideration of hydrogen economy in an effort to develop safe clean and reliable alternative energy sources for fossil fuels. Ammonia is one of the promising candidates due to its low production cost, ease in liquefaction at ambient temperatures, and high energy density as compared to methanol. Ammonia has a high content of hydrogen atoms per unit volume and can easily be cracked down into hydrogen and nitrogen. In the last four years carbon intensive coal dependent South Africa has become one of the leading global destinations for renewable energy investment. Another driving force behind the technology is the prevalence of platinum reserves found in South Africa. Platinum group metals are the key catalytic materials used in most fuel cells, and with more than 75 % of the world’s known platinum reserves found within South Africa. In this thesis, I have developed novel electrocatalysts that are highly specific and selective for production of hydrogen using ammonia as a fuel source. The electro-oxidation of ammonia on platinum electrode drop coated platinum nanoparticles (PtNP), platinum iridium nanoparticles (PtIrNP), platinum ruthenium nanoparticles (PtRuNP), platinum telluride nanoparticles (PtTeNP) and ternary nanoparticles (PtIrTeNP) finally (PtRuTeNP) was systematically studied in alkaline solution of potassium hydroxide (KOH) by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrocatalysts were synthesised using sodium borohydride as a reducing agent and polyvinylpyrrolidone (PVP) as a stabilising agent from aqueous solutions of H2PtCl6/IrCl3/RuCl3/NaHTe mixtures. XRD confirmed that the binary and ternary electro-catalyst displayed characteristic patterns which indicated that all catalysts have shown the Pt face-centred-cubic (fcc) crystal structure and that the nanoparticles were poly-orientated. The structural characterization was further confirmed with FTIR and UV-vis, FTIR showed the most striking evidence that the PVP stabilized Pt presented a broad peak between 1288 cm-1 and 1638 cm‐1 which corresponded to C‐N stretching motion and C=O stretching motion of monomer for PVP, respectively. The narrow absorption peak centered at 1420 cm‐1 and 2880 cm‐1 occurred in which was ascribed to the C–H bonding due to the presence of PVP. This was due to the formation of coordinate bond between the nitrogen atom of the PVP and the Pt2+, Ir3+, Ru3+ and Te2+ ions. UV-vis was able to show the oxidation state of the nanoparticles and obtained an exponential graph shape which indicated complete reduction because there was no peak observed. Morphological characterization in the form of high resolution scanning electron microscope (HRSEM) revealed the formation of poly-orientated nanoparticles with average particle size of 23- 46 nm with slightly aggregated crystalline materials. The elemental composition of the alloy nanoparticles measured using energy dispersive spectroscopy (EDS) showed the presence of the four elements; Pt, Ir, Ru and Te. High resolution transmission electron microscopy (HRTEM) revealed the formation of crystalline non-aggregated 0.6-5 nm sized nanoparticles. The elemental composition of the alloy nanoparticles measured using energy dispersive X-ray (EDX) showed the presence of the four elements; Pt, Ir, Ru and Te. Selected area electron diffraction pattern (SAED) nanoparticles showed characteristic electron diffraction rings of Pt, PtIr, PtRu, PtTe, PtIrTe and PtRuTe, confirmed the phase and crystallinity of the materials. The electrocatalytic behaviour of the PtIrTe and PtRuTe nanoparticles for ammonia oxidation in KOH solution showed reduced overpotential properties and an increased current density compared to the bare Pt nanoparticles electrode thus providing a promising alternative for development of low-cost and high-performance electrocatalyst for electro-oxidation of ammonia. In terms of minimising the ammonia oxidation overpotential, catalyst selection were ranked as follows PtTe > PtRuTe > PtIr > PtRu > PtIrTe > Pt, with regards to maximising the exchange current density, the ranking was PtTe > PtIrTe > Pt > PtRu > PtIr > PtRuTe. The results were further interrogated with EIS which revealed in terms of minimising charge transfer resistance (Rct) the nano catalysts selection were ranked as follows PtRuTe ˃ PtIrTe ˃ PtRu ˃ PtIr ˃ Pt ˃ Bare Pt electrode ˃ PtTe. That meant that the conductivity of the catalysts facilitated the flow of charge through the nanoalloys onto the surface of the electrode. The difference in charge transfer resistance revealed that PtRuTe and PtIrTe nanoalloys had an obvious advantage in reaction activity. The application of ternary metal nanoparticles had significantly enhanced the catalytic activity toward ammonia oxidation. The role of the third component (Te) had improved the catalysts in reducing Nads adsorption on Pt. The enhanced catalytic activity has been attributed by a number of factors including the change in Pt–Pt inter atomic distance, number of Pt nearest neighbours, Pt 5d band vacancy, and Pt metal content on particle surface.

Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-25Bitstream added on 2014-06-13T19:12:28Z : No. of bitstreams: 1 souza_ne_me_araiq.pdf: 1760976 bytes, checksum: 35d3c54c182ee2f7f62063b88971e49e (MD5) / Com o intuito de avaliar a influência da presença de óxido na resposta eletrocatalítica para a oxidação de etanol, foram preparados quatro materiais constituídos de partículas metálicas de Pt ou liga PtSn, suportados sobre SnO2 e carbono, ou diretamente sobre carbono (Pt-SnO2/C, Pt/C, PtSn/C e PtSn-SnO2/C). As nanopartículas metálicas e as nanopartículas de SnO2 foram preparadas inicialmente em estado coloidal, em processos de síntese realizados separadamente para garantir bom controle das propriedades dos materiais. Os catalisadores foram caracterizados por difratometria de raios-X, espectroscopia de fotoelétrons induzidos por raios-X e espectroscopia de absorção de raios-X dispersivos. Os resultados mostraram que houve formação de liga PtSn nos catalisadores PtSn/C e PtSn-SnO2/C e a formação de SnO2 em todos os catalisadores modificados com estanho. Os catalisadores com liga PtSn apresentaram um preenchimento da banda 5d da platina, enquanto que a modificação com SnO2 ocasionou um esvaziamento da banda. Experimentos de oxidação de CO adsorvido mostraram que os materiais possuem diferentes características superficiais, e que os catalisadores contendo liga PtSn têm menores areas de Pt eletroquimicamente ativa. A atividade catalítica para a oxidação de etanol foi avaliada por voltametria cíclica e cronoamperometria, que evidenciaram um melhor desempenho para os materiais PtSn/C e PtSn-SnO2/C. Os resultados obtidos indicam que a liga PtSn é fundamental para a promoção da atividade catalítica de oxidação de etanol em sistemas PtSn. / Aiming to evaluate the influence of oxides on the electrocatalytic activity for ethanol oxidation, four catalysts containing metallic Pt or PtSn nanoparticles supported either on SnO2 and carbon; or directely on carbon (Pt-SnO2/C, Pt/C, PtSn/C, and PtSn-SnO2/C) were prepared. Metallic nanoparticles and SnO2 nanoparticles were obtained, initially in colloidal state, in separate synthesis procedures to ensure adequate control of their properties. All catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and dispersive X-ray absorption spectroscopy. The results showed that a PtSn alloyed phase was formed on the PtSn/C and PtSn-SnO2/C catalysts and the presence of SnO2 in all materials containing tin. The two catalysts containing PtSn alloy showed a more filled Pt 5d band, while the addition of SnO2 produced a vacancy increase of the d band. Experiments of adsorbed CO oxidation showed that the catalyts have different surface characteristics, and that materials containg a PtSn alloyed phase have lower Pt electrochemically active areas. The catalytic activity for ethanol oxidation was evaluated by cyclic voltammetry and chronoamperometry, evidencing a better performance for PtSn/C and PtSn-SnO2/C. The results obtained indicate that the presence of PtSn alloy is necessary to enhance the catalytic activity for ethanol oxidation on PtSn systems

Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-06-17Bitstream added on 2014-06-13T19:53:28Z : No. of bitstreams: 1 gallo_ibc_me_araiq_parcial.pdf: 445176 bytes, checksum: 410960aab27a523d5f73c6228b215e75 (MD5) Bitstreams deleted on 2015-05-28T14:25:10Z: gallo_ibc_me_araiq_parcial.pdf,. Added 1 bitstream(s) on 2015-05-28T14:26:14Z : No. of bitstreams: 1 000721748_20150615.pdf: 421882 bytes, checksum: 1a30cf50cba3d066285c9085b7fc9b12 (MD5) Bitstreams deleted on 2015-06-15T12:50:19Z: 000721748_20150615.pdf,. Added 1 bitstream(s) on 2015-06-15T12:50:53Z : No. of bitstreams: 1 000721748.pdf: 3550801 bytes, checksum: f00aa1f6de99b8becd25ffedf524e967 (MD5) Bitstreams deleted on 2015-06-19T10:36:53Z: 000721748.pdf,. Added 1 bitstream(s) on 2015-06-19T10:37:28Z : No. of bitstreams: 1 000721748.pdf: 3550801 bytes, checksum: f00aa1f6de99b8becd25ffedf524e967 (MD5) / Neste trabalho foram sintetizadas nanopartículas de Pt, PtFe, PtNi, PtCo, PtFeNi e PtFeCo suportadas em pó de carbono através do método da microemulsão, que foram testadas como potenciais eletrocatalisadores frente a reação de redução do oxigênio (RRO). As propriedades eletrônicas dos materiais foram investigadas por XAS (Espectroscopia de Absorção de Raios X) e as propriedades estruturais e morfológicas por DRX (Difração de Raios X) e MET (Microscopia Eletrônica de Transmissão), respectivamente. A área superficial de platina eletroquimicamente ativa foi determinada a partir de dados de voltametria cíclica, enquanto a atividade eletrocatalítica para a RRO foi estudada em soluções de H2SO4 saturadas com O2, utilizando a técnica do eletrodo de disco rotatório. Em geral, a análise dos materiais binários e ternários mostrou uma diminuição no parâmetro de rede em relação à platina pura, o que é um indicativo da formação de liga. O método de síntese escolhido permitiu a obtenção de cristalitos com faixa de tamanhos em torno de 3 nm. Somente os materiais contendo nanopartículas trimetálicas apresentaram alto grau de aglomeração e uma distribuição não homogênea sobre o carbono suporte. As análises eletroquímicas sugerem que a RRO segue majoritariamente o mecanismo via 4 elétrons em todos os catalisadores estudados nesse trabalho. O estudo das propriedades eletrônicas indica que a presença de Fe, Ni e Co contribui para o preenchimento da banda 5d da platina. Todas estas informações foram correlacionadas na tentativa de se entender a razão pela qual os catalisadores trimetálicos, principalmente o PtFeCo/C, apresentaram atividade superior para a RRO quando comparados com os bimetálicos e a Pt/C. Os materiais ternários foram submetidos a tratamento térmico a 150 ºC em atmosfera de H2 por uma hora... / In this work, nanoparticles of Pt, PtFe, PtNi, PtCo, PtFeNi and PtFeCo supported on carbon powder were synthesized by a microemulsion method and tested as potential electrocatalysts for the oxygen reduction reaction (ORR). The electronic properties of the materials were investigated by XAS (X-ray Absorption Spectroscopy) and the structural and morphological properties by XRD (X-ray diffraction) and TEM (Transmission Electronic Microscopy), respectively. The platinum electrochemically active surface area was determined from cyclic voltammetry data while the electrocatalytic activity toward the ORR was studied using the rotating disk electrode technique in O2 saturated H2SO4 solutions. Overall, the analyses of the materials showed a decrease in the lattice parameter when compared to pure Pt, which suggests alloy formation. The chosen synthesis method allowed obtaining small crystallites with average size around 3 nm. Only the catalysts containing trimetallic nanoparticles were highly agglomerated and showed an inhomogeneous distribution of particles on the carbon support. The electrochemical analyses suggest that the ORR occurs mainly through the 4 electron mechanism on all catalysts studied in this work. The study of the electronic properties evidenced that the presence of Fe, Ni and Co increases the platinum 5d-band occupancy. All results were correlated aiming a better understanding of why the trimetallic catalysts, particularly PtFeCo/C, have significantly higher ORR activity than bimetallic materials and Pt/C. The trimetallic catalysts were heat treated at 150 ºC in a H2 atmosphere during one hour. As a result, the materials showed a minor increase in alloying degree, an increase in particle size, a slightly decrease in surface area and a more filled Pt 5d-band. Thermal treatment did not cause any... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:25:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-02-21Bitstream added on 2014-06-13T19:32:52Z : No. of bitstreams: 1 souza_rff_me_araiq_parcial.pdf: 309974 bytes, checksum: 62280d3f9acf765ce72f300ca525dbbb (MD5) Bitstreams deleted on 2015-04-01T12:51:13Z: souza_rff_me_araiq_parcial.pdf,Bitstream added on 2015-04-01T12:51:47Z : No. of bitstreams: 1 000718974.pdf: 1705233 bytes, checksum: 959b8b3cc41bf702fc47d575d0eddbfc (MD5) / Células a combustível são dispositivos promissores devido a sua alta eficiência na conversão de energia química em energia elétrica com baixo ou nenhum impacto ambiental. O desempenho das células de baixa temperatura de operação depende, dentre outros fatores, do catalisador utilizado, composto geralmente de platina na forma de nanopartículas suportadas sobre carbono de alta área superficial. Metanol é um dos combustíveis que pode ser empregado nas células, no entanto sua eletro-oxidação gera espécies intermediárias, como o CO, que permanecem fortemente adsorvidas nos sítios da platina “envenenando” o catalisador, e que são oxidadas apenas em potenciais elevados. O presente trabalho consistiu na preparação de nanopartículas de PtRuM/C (M = Fe ou Sn) ancoradas sobre carbono de alta área superficial, analisando a influência do terceiro metal na atividade eletrocatalítica frente à reação de oxidação de metanol. Os catalisadores foram preparados pelo método de microemulsão e tratados termicamente em atmosfera inerte. A caracterização das propriedades físicas foi realizada por difratometria de raios X (DRX), microscopia eletrônica de transmissão (TEM), espectroscopia de fotoelétrons excitados por raios X (XPS) e espectroscopia de absorção de raios X dispersivos (DXAS). O comportamento eletroquímico geral dos catalisadores foi avaliado por voltametria cíclica em meio ácido e a atividade eletrocatalítica para a de oxidação de metanol foi estudada por varredura linear de potencial e cronoamperometria. A análise dos produtos e intermediários da oxidação de metanol foi realizada quantitativamente e qualitativamente por cromatografia líquida de alta eficiência (HPLC) e espectroscopia de infravermelho por transformada de Fourier (FTIR) in-situ. Os resultados para eletro-oxidação de metanol demonstram que... / Fuel cells are promising devices because of its high efficiency in converting chemical energy to electrical energy with low or no environmental impact. The cell performance depends, among other factors, on the catalysts used, usually consisting of platinum nanoparticles supported on high surface area carbon. Methanol is one of the fuels that can be used in a fuel cell. However, its electro-oxidation produces intermediate species, such as CO, which remain strongly adsorbed on the platinum sites, poisoning the catalyst surface because their oxidation takes place only in high potentials. In this work, PtRuM/C (M = Fe or Sn) nanoparticles supported on high surface area carbon were prepared and the influence of the third metal in the electrocatalytic activity toward methanol oxidation was analyzed. The catalysts were prepared in microemulsions and heat treated in an inert atmosphere. Characterization of physical properties was performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and dispersive X-ray absorption spectroscopy (DXAS). The general electrochemical behavior of the catalysts was evaluated by cyclic voltammetry in acidic solution while the electrocatalytic activity for methanol oxidation was studied by linear potential sweeps and chronoamperometry. Analysis of the products of methanol oxidation was performed qualitatively and quantitatively by high performance liquid chromatography (HPLC) and in-situ Fourier transformed infrared spectroscopy (FTIR). The results for the electro-oxidation of methanol demonstrate that addition of Sn improves the activity of the materials, while the presence of Fe is detrimental. Moreover, data also revealed that heat treatment promoted... (Complete abstract click electronic access below)

Made available in DSpace on 2014-11-10T11:09:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-06-05Bitstream added on 2014-11-10T11:57:26Z : No. of bitstreams: 1 000783685_20160605.pdf: 417557 bytes, checksum: a7b0b5d0342ef5b2b95ede9798577d33 (MD5) Bitstreams deleted on 2016-06-06T12:04:13Z: 000783685_20160605.pdf,. Added 1 bitstream(s) on 2016-06-06T12:05:00Z : No. of bitstreams: 1 000783685.pdf: 2427704 bytes, checksum: a17d8f00bffa113ed4ce546928b1d574 (MD5) / Este trabalho visou contribuir ao desenvolvimento de materiais com bom desempenho para a catálise da reação de redução de oxigênio, que ocorre nos cátodos de células a combustível, através do estudo da influência da composição e da nanoestrutura de nanopartículas de PtNi suportadas em carbono na atividade eletrocatalítica. Os estudos envolveram a preparação de catalisadores contendo nanopartículas de PtNi com diferentes composições pelo método do poliol modificado. Partes destes materiais foram submetidas a tratamento térmico em hidrogênio a 300ºC com o intuito de promover um aumento da incorporação de Ni na rede da Pt sem provocar severas modificações no tamanho e distribuição das nanopartículas sobre o suporte. As propriedades físicas dos materiais foram estudadas pelas técnicas de difração de raios X e microscopia eletrônica de transmissão. Os resultados mostraram que os catalisadores de PtNi têm um elevado grau de liga e boa homogeneidade de distribuição das partículas sobre o carbono suporte. As propriedades eletrônicas foram avaliadas por espectroscopia de absorção de raios X in situ. A atividade eletrocatalítica para a redução do oxigênio foi estudada utilizando-se a técnica de eletrodo de disco-anel rotatório. Em meio ácido, a presença de Ni nos catalisadores promove um aumento da vacância da banda 5d da Pt, ao tempo que o tratamento térmico provoca uma diminuição da vacância em relação aos materiais como preparados. Foi verificada uma maior atividade catalítica dos materiais de PtNi em relação à Pt. Em meio alcalino, os catalisadores que contêm Ni mostraram a banda 5d mais preenchida, provavelmente resultado da formação de óxidos de Ni. De modo geral, os catalisadores PtNi são menos ativos que a Pt em meio alcalino. A tolerância à presença de metanol foi avaliada através de comparação entre as curvas de polarização obtidas em soluções ácida e alcalina com as... / This study aimed to contribute to the development of materials with good performance for the catalysis of the oxygen reduction reaction, which occurs at the cathodes of fuel cells, by studying the influence of composition and nanostructure of carbon-supported PtNi nanoparticles on the electrocatalytic activity. The studies involved the preparation of catalysts containing PtNi nanoparticles of different compositions by the modified polyol method. Parts of these materials were submitted to a heat treatment in hydrogen at 300 °C aiming to promote an increase of the incorporation of Ni into the Pt lattice without causing severe changes on the size and distribution of particles on the support. The physical properties of the materials were evaluated by X-ray diffraction and transmission electron microscopy. The results showed that PtNi catalysts have a high degree of alloying and that particle distribution on the carbon support has good homogeneity. The electronic properties were evaluated in situ by X-ray absorption spectroscopy. The electrocatalytic activity for the oxygen reduction reaction was studied by the rotating ring disk technique. In acid medium, the presence of Ni in the catalysts causes an increase in the Pt 5d band, while the heat treatment resulted in a Pt 5d band vacancy decrease. A catalytic activity for PtNi materials higher than that of Pt was verified. In alkaline medium, the catalysts containing Ni showed a Pt 5d band more filled, probably resulting from the formation of Ni oxides. In general, Pt Ni catalysts are less active than Pt in alkaline medium. The tolerance to the presence of methanol was evaluated by comparing the polarization curves obtained in acid and alkaline solutions containing alcohol. A decrease of catalytic activity in the presence of methanol in acid medium and good tolerance in alkaline medium were observed.

Made available in DSpace on 2014-06-11T19:29:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-02-28Bitstream added on 2014-06-13T18:38:50Z : No. of bitstreams: 1 cumba_lr_me_ilha.pdf: 1172695 bytes, checksum: 022bcc613710f630671a10681e48bedb (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho descreve a preparação, caracterização e aplicação eletroanalítica de um compósito formado por Titânio fosfatado modificado com metais de transição (Ag1+, Co2+ e Ni2+) e hexacianoferrato de potássio. A primeira etapa consistiu em reagir o isopropóxido de titânio (IV) com H3PO4, sendo que o material obtido foi descrito como TiP. Em uma segunda etapa reagiu-se o TiP com íons metálicos, originando TiPM (M = Ag1+, Co2+ e Ni2+). Algumas técnicas espectroscópicas como espectroscopia vibracional (FT-IR), Difração de Raios X (DRX), Espectroscopia na região do ultravioleta visível (UV-Vis por Reflectância difusa)e Voltametria cíclica foram utilizadas na caracterização do TiP e do TiPMH. Os espectros na região do Infravermelho dos materiais supracitados exibiram freqüências em 2112 cm-1 para o TiPAgH, 2136 cm-1 para o TiPCoH e um a 2168 cm-1 e outro a 2099 cm-1 para o TiPNiH, atribuídas ao estiramento (C≡N) característico do hexacianoferratos de prata, cobalto e níquel. Através dos difratogramas pode se verificar a diferença de cristalinidade dos complexos binucleares formados. A Espectroscopia na região do ultravioleta visível (UV-Vis por Reflectância difusa)das espécies suportadas, TiPCoH, após deconvolução espectral, exibiu claramente duas absorções com comprimento de onda máximo (max) em 437 e 504 nm para o TiPCoH, em 421 a 461 nm para o TiPAgH e em em 423 e 433 nm para o TiPNiH. Por fim, efetuou-se um estudo eletrocatalítico de substâncias de interesse biológico, utilizando um eletrodo de pasta de grafite modificado com TiPMH, após um rigoroso estudo sobre o comportamento voltamétrico dos mesmos. O eletrodo de pasta de grafite contendo o TiPAgH exibiu um par redox com potencial médio (E’) de: (E’) = 0,77V vs Ag/AgCl atribuído ao processo... / The present work describes the preparation, characterization and electroanalytical application of a composite consisting of titanium phosphate modified with transition metals (Ag1+, Co2+ and Ni2+) and potassium hexacyanoferrate. The first step consisted in reacting the titanium isopropoxide (IV) with H3PO4, being that the material obtained was described as TiP. In a second step if the TiP reacted with metal ions, giving TiPM (M = Ag1+, Co2+ and Ni2+). Some techniques such as vibrational spectroscopy (FT-IR), X-ray diffraction (XRD), Diffuse Reflectance and cyclic voltammetry were used to characterize the TiP and TiPMH. The spectra in the region of Infrared of materials abovementioned exhibited frequencies in 2112 cm -1 for TiPAgH, 2136 cm-1 for TiPCoH and one to 2168 cm-1 and another to 2099 cm-1 for TiPNiH, attributed to stretching (C ≡ N) characteristic of hexacyanoferrates of silver, cobalt and nickel. Through the diffractograms can verify the difference of crystallinity of the complexes binuclear formed. The diffuse reflectance of species supported after spectral deconvolution, clearly showed two absorptions with peak wavelength ( max) at 437 and 504 nm for TiPCoH at 421 and 461 nm for TiPAgH and in 423 and 433 nm for the TiPNiH. Finally, we performed an electrocatalytic study of substances of biological interest, using a carbon paste electrode modified with TiPMH, after a rigorous study on the voltammetric behavior of the same. The carbon paste electrode containing TiPAgH exhibited a redox couple with average potential (E') of (E') = 0.77 V vs Ag/AgCl(s) redox process attributed to FeII(CN)6 / FeIII(CN)6 in presence of silver. The carbon paste electrode modified with TiPAgH showed electrocatalytic activity for three substances of biological interest... (Complete abstract click electronic access below)