Graphene has great potential for energy storage and conversion applications due to its outstanding electrical conductivity, large surface area and chemical stability. However, the pristine graphene offers unsatisfactory performance as a result of several intrinsic limitations such as aggregation and inertness. The functionalization of graphene is considered as a powerful way to modify the physical and chemical properties of graphene, and improve the material performance, which unfortunately still being preliminary and need further knowledge on controllable functionalization methods and the structure-property relationships. This thesis aims to provide in-depth understanding on these aspects. We firstly explored oxygen-functionalized graphene for supercapacitor electrodes. A mild solvothermal method was developed for graphene preparation from the reduction of graphene oxide; the solvent-dependent reduction kinetics is an interesting finding in this method that could be attributed to the solvent-graphene oxide interactions. Using the solvothermal method, oxygen-functionalized graphene with controlled density of oxygen functional groups was prepared by tuning the reduction time. The oxygen-containing groups, primarily phenols and quinones, reduce the graphene aggregation, improve the wetting properties and introduce the pseudocapacitance. Consequently, excellent supercapacitive performance was achieved. Nitrogen-doped graphene was synthesized by the pyrolysis of graphene oxide with nitrogen-containing molecules and used as an electrocatalyst for oxygen reduction reactions. We achieved the structural control of the nitrogen-doped graphene, mainly the content of graphitic nitrogen, by manipulating the pyrolysis temperature and the structure of nitrogen-containing molecules; these experiments help understand the evolution of the bonding configurations of nitrogen dopants during pyrolysis. Superior catalytic activity of the prepared nitrogen-doped graphene was found, due to the enriched content of graphitic nitrogen that is most active for the oxygen reduction reaction. Moreover, we demonstrated a facile strategy of producing superhydrophobic octadecylamine-functionalized graphite oxide films. The long hydrocarbon chain in octadecylamine reduces the surface energy of the graphene oxide film, resulting in a high water contact angle and low hysteresis. The reaction mechanism and the effect of hydrocarbon chain length were systematically investigated. In addition to the researches on graphene-based materials, some results on advanced carbon nanomaterials and polymer composites for electronic packaging will also be discussed as appendix to the thesis. These include carbon nanotube-based capacitive deionizer and gas sensor, and hexagonal boron nitride-epoxy composites for high thermal conductivity underfill.

Thesis (M.S.)--Ohio University, August, 2006. / Title from PDF t.p. Includes bibliographical references.

Made available in DSpace on 2014-06-11T19:23:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-28Bitstream added on 2014-06-13T18:09:36Z : No. of bitstreams: 1 scachetti_tp_me_bauru.pdf: 1191066 bytes, checksum: 5b80315fb832aa7768b76bd2966dd871 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fases intermetálicas ordenadas de platina e de alguns metais de transição, Pt-M (M = Mn, Mo, Pb, Sb e Sn), são propostas como materiais eletrocatalisadores para serem utilizadas em células a combustível de oxidação direta de etanol pela possibilidade de unir, nestes materiais, a excelente capacidade de adsorção dos combustíveis orgânicos pelos sítios de platina e a menor susceptibilidade de bloqueio dos sítios dos metais de transição por intermediários e produtos de reação. O procedimento experimental usado na obtenção das fases intermetálicas ordenadas foi a fusão dos metais puros em um forno a arco voltaico, sob atmosfera de argônio, pesados em proporção estequiométrica 1:1, com posterior re-fusão dos materiais em um forno de indução térmica e tratamento térmico por 24h na temperatura de estabilização da fase. Os materiais obtidos foram caracterizados pelas técnicas de Difração de Raios-X (DRX), Microscopia Eletrônica de Varredura com Energia Dispersiva de Fluorescência de Raios-X (MEV-EDX) e Espectroscopia Fotoeletrônica de Raios-X (XPS), cujos resultados indicaram que a metodologia utilizada levou a obtenção de materiais com excelentes características de compactação e homogeneidade, não apresentando segregação de fases e variação desprezível de composição. A avaliação da atividade eletrocatalítica destes materiais para a reação do etanol foi realizada empregando... / Ordered intermetallic platinum phases with several transition metals, Pt-M (M = Mn, Mo, Pb, Sb e Sn), have been proposed as electrocatalytic materials to be used in direct ethanol fuel cells, as they combine an excellent capacity to adsorb organic fuels at the platinum sites with the low susceptibility to being poisoned by intermediates and reaction products at the transition-metal sites. The experimental procedure used to obtain the ordered intermetallic phases was the melting of the pure metals weighed in 1:1 molar stoichiometric proportion in an electric-arc furnace, under an argon atmosphere, afterwards the materials were re-melted in a thermal induction furnace and annealed for 24h at the temperature at which the desired phase is stable. The phases thus produced were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy with surface analysis by Energy-Dispersive X-ray Spectrometry (SEM-EDX), Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS) and these results showed that the methodology used was succeeded in obtaining ordered intermetallic platinum phases with a high level of homogeneity, no detectable phase segregation and no significant composition variation. The evaluation of the electrocatalytic activity of these materials for the ethanol oxidation reaction was performed by cyclic voltammetry and chronoamperometry techniques... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-06-28Bitstream added on 2014-06-13T18:09:39Z : No. of bitstreams: 1 goncalves_brl_me_bauru.pdf: 1866198 bytes, checksum: 6cb837c9d2ac03ec4728070b23227b74 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / 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... / 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)

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-04-19Bitstream added on 2014-06-13T18:50:39Z : No. of bitstreams: 1 antoniassi_bs_me_bauru.pdf: 1977733 bytes, checksum: 9dd271c973d63a540d0f517fcfe56409 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O grande desafio a ser vencido para a utilização de células a combustível de oxidação direta de álcoois (DAFC) refere-se ao desenvolvimento de eletrocatalisadores que favoreçam a oxidação direta do combustível a CO2 e que sejam menos susceptíveis ao envenenamento por intermediários/produtos de reação. Fases intermetálicas ordenadas de Pt têm sido propostas como materiais eletrocatalisadores para estas reações pelo fato de poderem aliar a excelente capacidade de adsorção do orgânico pelos sítios de platina e minimizarem a ação de bloqueadores superficiais. Não menos importante, essa classe de materiais apresenta uma estabilidade físico-química acentuadamente superior a materiais obtidos por deposição de íons metálicos e, desta forma, é mais apropriada para ser empregada diretamente em sistemas reais. Baseado em estudos anteriores a respeito dos materiais obtidos por deposição de íons metálicos sobre a superfície de platina e também estudos preliminares de oxidação de orgânicos em fases intermetálicas ordenadas de PtBi, este trabalho apresenta os resultados obtidos através do estudo da eletrocatálise das reações de oxidação do ácido fórmico e do metanol sobre as fases intermetálicas PtMn, PtMo, PtPb, PtSb e PtSn, em meio ácido... / The great challenge to be won for the use of direct oxidation of alcohols fuel cells (DAFC) refers to the electrocatalytic development that favor the direct oxidation of the fuel CO2 and that are less susceptible to the poisoning by intermediates/products of reaction. Ordered intermetallic phases of Pt have been proposed as electrocatalytic materials for these reactions for the fact of they could ally the excellent capacity of adsorption of the organic for the platinum sites and they minimize the action of blocking superficial. No less important, that class of materials presents a physicochemical stability strongly to materials obtained by deposition of metallic íons and, this way, it is more appropriate to be used directly in real systems. Based on previous studies regarding the materials obtained by deposition of metallic íons on the platinum surface and also preliminary studies of oxidation of organic in ordered intermetallic phases of PtBi, this work presents the results obtained through the study of the electrocatalysis of the reactions of oxidation of the formic acid and of the methanol on the intermetallic phases PtMn, PtMo, PtPb, PtSb and PtSn, in acid middle... (Complete abstract, click eletronic address below)

No description available.

Orientador: Prof. Dr. Mauro Coelho dos Santos / Tese (doutorado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência e Tecnologia/Química, 2015. / Eletrocatalisadores PtSnNi foram preparados pelo método dos precursores poliméricos (MPP) em diferentes proporções metálicas e suportados em carbono de alta área superficial, com 20% de metal em massa, para serem estudados na reação de oxidação de etanol (ROE). O material que se apresentou mais promissor para a reação de oxidação eletroquímica de etanol, PtSnNi/C na razão atômica (33:21:46), foi submetido a testes acelerados de estresse (TAE) com perda de aproximadamente 50% da corrente de oxidação em cronoamperometria. Após os TAE, foram observadas mudanças na formação de produtos de oxidação de etanol, determinados por FTIR-ATR in situ, que passaram de acetaldeído e ácido acético para somente acetaldeído. Dada esta condição, nanotubos de carbono de paredes múltiplas funcionalizados com grupos carboxílicos (NTC) também foram utilizados como suporte para PtSnNi/NTC (33:21:46) com 20% de metal em suporte preparado também pelo MPP. Desta forma, os eletrocatalisadores foram estudados em termos da dissolução de seus metais por técnicas de eletrodo de disco rotatório (EDR) e microcélula eletroquímica de fluxo de varredura (CFV) utilizando-se ICP-MS. Foi observado um decréscimo de somente 4% da área superficial eletroquimicamente ativa (ASE) do PtSnNi/NTC e 3% do material comercial PtSn/C E-TEK, enquanto que para PtSnNi/C houve uma diminuição de 32% da ASE para oxidação de CO. Com a confirmação da dissolução dos metais, é sugerida uma mudança na formação de produtos da oxidação de etanol já a partir da fase inicial da ciclagem, este efeito se corrobora ao se analisar o aumento da produção de acetaldeído no eletrocatalisador PtSnNi/C por FTIRATR in situ. Adicionalmente, nos testes realizados em condições operacionais de células a combustível de etanol direto (DEFC), foi observado que PtSnNi/NTC apresentou menor decaimento de potencial durante a curva de polarização, fato que pode estar relacionado tanto a estabilidade do suporte e interação com os metais (que apresentaram menor dissolução) bem como pela seletividade na formação dos produtos, determinados por cromatografia a gás, que também se mantém constante. Onde PtSnNi/NTC apresenta seletividade de aproximadamente 60 e 40% para acetaldeído e ácido acético, respectivamente. Enquanto PtSnNi/C apresentou seletividade somente para acetaldeído. / PtSnNi electrocatalysts were prepared by polymeric precursors method (PPM) with different metallic ratios supported on carbon Vulcan® to obtain 20 % (m/m) of metal loading and studied for ethanol oxidation reaction (EOR). The more promising material for the ethanol electrochemical oxidation reaction, PtSnNi/C (33:21:46 atomic ratio), was submitted to accelerated stress tests (AST) with a loss of approximately 50% of the chronoamperometric current of oxidation. After AST, changes were observed on the formation of ethanol oxidation products, determined by FTIR-ATR in situ, from acetaldehyde and acetic acid to acetaldehyde formation, exclusively. Given this condition, multi-walled carbon nanotubes functionalized with carboxylic groups (CNT) were also used as support for PtSnNi/CNT (33:21:46) prepared by PPM with 20% of metal loading on support. Thus, the electrocatalysts were evaluated concerning the metals dissolution by rotating disk electrode (RDE) technique and microelectrochemical scanning flow cell (SFC) using ICP-MS. A decrease of only 4% of PtSnNi/CNT electrochemically active surface area (ECSA) was observed and 3% for the PTSn/C E-TEK commercial material. In contrast, the PtSnNi/C ECSA decreased 32% for CO oxidation. With the confirmation on metals dissolution, it is suggested a change in the formation of ethanol oxidation products already from the initial step of cycling, that can be corroborated with the acetaldehyde production increase on PtSnNi/C electrocatalyst by FTIR-ATR in situ analyses. Additionally, in direct ethanol fuel cells (DEFC) tests on operational conditions, it was observed that PtSnNi /CNT showed less decay of potential during polarization curve experiments, which may be related to support stability and interaction with metals (which presented lower dissolution) as well as the selectivity in the products formation for EOR, determined by gas chromatography, which also remained constant. So that PtSnNi/NTC showed selectivity of about 60 and 40% for acetaldehyde and acetic acid, respectively. While PtSnNi/C showed selectivity just for acetaldehyde.

Three types of electrodes: carbon paste electrodes modified with nanoparticles of metallophthalocyanines (MPcNP-CPEs, M = Mn, Fe, Ni, Co), basal plane pyrolytic graphite electrodes modified with iron or nickel phthalocyanine nanoparticles and multiwalled carbon nanotube composites (FePcNP/MWCNT-BPPGE or NiPcNP/MWCNT-BPPGE),and basal plane pyrolytic graphite electrodes modified with multiwalled carbon nanotubes and electropolymerized metal tetra-aminophthalocyanines (poly-MTAPc-MWCNT-BPPGE), where M is Mn, Fe, Ni or Co, were prepared. Electrochemical characterizations showed that faster electron transfer kinetics occurred at the NiPcNP/MWCNT-BPPGE than at the FePcNP/MWCNT-BPPGE surface. SEM and electrochemical characterizations of poly-MTAPc-MWCNT-BPPGE showed that MTAPc had been deposited on the MWCNTBPPGE surface, and that the poly-CoTAPc-MWCNT-BPPGE exhibited the fastest electron transfer kinetics of all the poly-MTAPc-MWCNT-BPPGEs. Using amitrole and asulam as test analytes, electrochemical experiments showed that, amongst the CPEs, the FePcNP-CPE and NiPcNP-CPE displayed the most electrocatalytic behavior towards amitrole and asulam oxidation, respectively, and further experiments were done to obtain the electrochemical parameters associated with these electrodes and the corresponding analytes. Although, the FePcNP/MWCNT- BPPGE displayed electrocatalytic behavior towards amitrole oxidation in comparison with the bare BPPGE, it was less electrocatalytic than the FePcNP-CPE in terms of detection potential. The NiPcNP/MWCNT-BPPGE displayed the same detection potential as the NiPcNP-CPE. The poly-FeTAPc-MWCNT-BPPGE exhibited the most electrocatalytic behavior towards amitrole, of all the electrodes investigated, and the poly-CoTAPc-MWCNT-BPPGE displayed the best electrocatalytic behavior towards asulam, amongst the poly-MTAPc-MWCNT-BPPGEs.

Metallophthalocyanines and metal nanoparticles were successfully synthesized and applied for the electrooxidation of amitrole, nitrite and hydrazine individually or when employed together. The synthesized materials were characterized using the following techniques: predominantly scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemistry and scanning electrochemical microscopy (SECM). Different electrode modification methods were used to modify the glassy carbon substrates. The methods include adsorption, electrodeposition, electropolymerization and click chemistry. Modifying the glassy carbon substrate with MPc (electropolymerization) followed by metal nanoparticles (electrodeposition) or vice versa, made a hybrid modified surface that had efficient electron transfer. This was confirmed by electrochemical impedance studies with voltammetry measurements having lower detection potentials for the analytes. This work also describes for the first time the micropatterning of the glassy carbon substrate using the SECM tip. The substrate was electrografted with 4-azidobenzenediazonium salt and then the click reaction was performed using ethynylferrocene facilitated by Cu⁺ produced at the SECM tip. The SECM imaging was then used to show the clicked spot.

Molybdenum disulfide (MoS2) has been demonstrated to be a potential catalyst in the hydrogen evolution reaction (HER). Due to its highly active edge site, abundance, and low cost, it rivals Pt. However, the potential activity of the MoS2 basal plane has largely been ignored. The physical characteristics of MoS2 and its corresponding band structure change significantly with decreasing thickness, especially at the monolayer limit. Thus, an investigation on the thickness dependence may provide important insights into the MoS2 basal plane activity. In this thesis, the layer dependent electrocatalytic performance is investigated with mono-, bi- and multilayer MoS2 based individual nanodevices. Three conclusions were reached. (1) Monolayers showed exchange current densities more than one order of magnitude higher than that of the multilayers, 0.12 mA/cm2 and 8.7 mA/cm2, respectively. Furthermore, the onset potential of the monolayer was several hundred millivolts lower than that of the multilayer, about 0.2 V vs RHE for the monolayer versus 0.5 V vs RHE for the multilayer. The Tafel slope of 100-200 mV/dec revealed that the rate limiting step was the adsorption of hydrogen. (2) Interestingly, the bilayer sample exhibited an increase in its exchange current density from 0.3 mA/cm2 to 8 mA/cm2 when cycled extensively. This is suspected to be caused by intercalation of hydrogen between the atomic layers. (3) Additionally, the back-gate voltage is applied to tune the Fermi level of the material and the catalytic performance. It was found that the back-gate voltage induces an irreversible change in all samples, increasing the exchange current density by an order of magnitude. The superior basal plane performance of the monolayers to that of the multilayers reveals a new way to optimize the performance of MoS2 as a HER catalyst. In addition, the results above illuminate the yellow brick road to potential improvements in other layered materials as well.