In this work, two catalysts, lanthanum manganite strontium-doped perovskite without (LSM) and with (LSMMO) mixed molybdenum oxides, were synthesized by the sol-gel route and deposited by immersion in carbon cloth substrates. Their performance as cathodes in the hydrogen peroxide reduction reaction (HPRR) and oxygen reduction reaction (ORR) was investigated through cyclic voltammetry and electrochemical impedance spectroscopy, the electrocatalytic efficiency of these electrodes in the HPRR was analyzed in KOH and H2O2 medium at 298 K. The performance of the cathodes, in a single compartment, using a nickel plate as an anode was also investigated. The results showed that for the reduction reactions, electrodes developed with LSMMO have more significant catalytic activity than LSM after polarization, resulting in 32% higher current densities, lower electrical resistance after polarization, and a 21% increase in power density.

RESUMO Um dos desafios atuais é a busca de materiais eficientes e de baixo custo para os componentes das Pilhas a Combustível de Óxido Sólido (PaCOS), já que estes dispositivos se destacam pela geração limpa de energia elétrica e alta eficiência. Dentre estes componentes está o interconector, nos quais o aço inoxidável ferrítico poderia ser utilizado na sua fabricação. No entanto revestimentos protetores são necessários para bloquear a volatilidade do cromo da superfície metálica do interconector nas condições de operação das PaCOS. Neste trabalho, os revestimentos foram obtidos a partir de soluções eletrolítica contendo Co2+ e Mn2+ provenientes de catodos de baterias de íon lítio (BIL’s) exauridas. Foram feitas eletrodeposições potenciostáticas com o objetivo de se obter ligas de cobalto e manganês sobre a superfície de amostras do aço AISI 430. Dados de eficiência de carga do processo foram calculados para otimização das amostras, e a condição de pH mais ácido (pH=3) mostrou-se menos eficiente. Contudo, o filme apresentou microestrutura homogênea, menos porosa e constituída por uma camada interna de (Mn, Cr)2O3 e externa de MnCo2O4, capaz de bloquear a perda do Cr, conforme mostraram as análises de DRX, MEV e EED. Já para o pH menos ácido (pH=3,5), não foi identificada a presença do Mn na composição do depósito, e o revestimento formado de Co3O4 não se mostrou capaz de bloquear a perda de cromo por volatilidade.

ABSTRACT One of the current challenges is the search for efficient and low-cost materials for the components of Solid Oxide Fuel Cells (SOFCS), since these devices stand out for the clean generation of electric energy and high efficiency. Among these components is the interconnector, ferritic stainless steel can be used in its manufacture. However, protective coatings are necessary to block the volatility of the chrome of the metallic surface of the interconnector under the operating conditions of the PaCOS. In this work, the coatings will be obtained from electrolytic solutions containing Co2+ and Mn2+ from cathodes of exhausted lithium-ion batteries (LIB’s). Potentiostatic electrodepositions will be performed to obtain cobalt and manganese alloys on the AISI 430 steel samples surface. The charge efficiency data were calculated to optimize the samples, and the more acidic pH condition was shown to be less efficient. However, the film showed a homogeneous microstructure, less porous and composed of an internal (Mn, Cr)2O3 layer and an external MnCo2O4 layer, capable of blocking the loss of Cr, as demonstrated by the analyzes of XRD, SEM and EDS. For the less acidic pH, the presence of Mn in the deposit composition was not identified, and the coating formed by Co3O4 was not able to block the loss of chromium by volatility.

Abstract This work reports the spectroelectrochemical and electrical behavior of electropolymerized donor-acceptor like (D-A) copolymer films, based on 3,4-ethylenedioxythiophene (EDOT) and beta-substituted electron-acceptor thiophenes. Initially, the copolymer films were deposited on indium tin oxide substrates, which spectroelectrochemistry measurements were carried out with an UV-Vis spectrophotometer. Hence, it was possible to observe the electrochromic properties of these materials, visualizing the color changing towards different potentials applied. The experiments have shown that these D-A like copolymers presented good electrochromic properties, such as optical contrast, coloration efficiency, and switching times. Additionally, films prepared on a platinum working electrode were investigated by electrochemical impedance spectroscopy, which has shown the electrical behavior of those copolymers and their potential as candidates to capacitive devices building. Therefore, the combination of electron-donor EDOT with those electron-acceptor monomers is indeed a useful strategy to tailoring and fine-tuning the physicochemical properties of polythiophenes with innovative applications.

A novel, fast, low-cost and scalable methodology to prepare stable magnetoliposomes (MGLs), without the use of organic solvents, is described. The concept of the work is based on the dual use of soy lecithin associated to a new liposome preparation methodology. Soy lecithin was used to coat the nanoparticles of magnetite (Fe3 O4 @lecithin) and for encapsulation of Fe3 O4 @lecithin (Lip-Fe3 O4 @lecithin). Liposomes with size less than 160 nm, polydispersity index of 0.25 and zeta potential of -41 mV, were prepared with the use of autoclave and sonication. The liposomal formulations containing magnetite and stigmasterol (Lip-Fe3 O4 @lecithin, Lip-Stigma and Lip-Stigma-Fe3 O4 @lecithin) were shown to be promising for the application as antibacterial. The liposomal formulation and magnetite were characterized by the following techniques: conventional and high-resolution transmission electron microscopy (TEM/HRTEM), energy-filtered transmission electron microscopy (EFTEM), proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD), dynamic light scattering (DLS) and zeta potential. The Lip-Fe3 O4 @lecithin had a minimum inhibitory concentration (MIC) of 8.4 µg mL-1 in the presence of 200 Oe magnetic field against S. aureus.

Abstract A practice used to prevent corrosion in buried slurry pipelines is the hibernation of pipelines with an aqueous solution containing corrosion inhibitors before beginning the mining operation. The aim of this work is to evaluate the corrosion resistance of API 5L X70 steel used in the slurry pipelines in hibernation solution containing sodium sulphite, sodium hydroxide and glutaraldehyde in a synthetic river water. The electrochemical techniques used are the Tafel analysis and electrochemical impedance spectroscopy. The synergistic effect of the components of hibernation solution on the corrosion resistance of the API 5L X70 steel was evaluated. A lower corrosion resistance was obtained for the API steel in aqueous solution of sodium sulphite, and in solution of sodium sulphite with glutaraldehyde. The hibernation solution was efficient in inhibiting steel corrosion but the highest corrosion inhibition efficiency was obtained with the glutaraldehyde aqueous solution.

Materials based on a mixture of poly(vinylidene fluoride) (PVDF), poly(2-hydroxyethyl methacrylate) (PHEMA) and LiClO4 were produced to evaluate their ionic behavior and morphological structure to determine if they can be used as an electrolyte in electrical devices. FTIR chemical analysis results indicated the presence of interactions between PVDF, PHEMA and LiClO4. MDSC results showed that the transition temperatures of the polymers shifted to higher temperatures for systems containing high concentrations of each polymer. SEM images indicated that there was some miscibility between the polymers especially for the 25 and 75 wt. % compositions. In terms of the electrical performance, the ionic conductivity level of the electrolyte could be controlled by changing the composition of the system.

Três polímeros e dois novos copolímeros baseados em derivados de politiofenos 3-substituídos têm sido estudados e todos demonstraram propriedades fotoluminescentes. Todos os polímeros sintetizados, poli(3-metoxitiofeno) (PMOT), poli(3-tiofenoetanol) (PTE), poli(3-tiofenometanol) (PTM), e copolímeros, poli(3-metoxitiofeno-co-3-tiofenoetanol) (PMOT-co-TE) e poli(3-metoxitiofeno-co-3-tiofenometanol) (PMOT-co-TM), foram caracterizados por FT IR, UV-Vis, fotoluminescência (PL), análise térmica (TG e DSC) e difração de raios X. Todos os materiais mostraram emissão de luz na região do laranja do espectro visível. A obtenção dos polímeros e copolímeros foi confirmada por análise espectrométrica na região do infravermelho. A análise térmica mostrou boa estabilidade térmica para os materiais obtidos.

This work reports the synthesis of three polymers and two new copolymers based on 3-substituted polythiophene derivatives, all of them demonstrated photoluminescent properties. All polymers synthesized, i.e., poly(3-methoxythiophene) (PMOT), poly(3-thiopheneethanol) (PTE), poly(3-thiophenemethanol) (PTM), poly(3-methoxythiophene-co-3-thiopheneethanol) (PMOT-co-TE) and poly(3-methoxythiophene-co-3-thiophenemethanol) (PMOT-co-TM), were characterized by FT IR, UV-Vis, photoluminescence (PL), thermal analysis (TG and DSC) and X-ray diffraction (XRD). All materials emitted light in the orange region of the visible spectrum. Spectrometric analysis in the infrared region demonstrated the successful synthesis of polymers and copolymers by the presence of characteristic bands. Thermal analysis showed that the obtained materials had good thermal stability.

In this review we summarize recent synthetic investigations about the preparation of oligothiophenes and polythiophenes, the most important π-conjugated organic materials for applications in electrochromic and electroluminescent devices. It is showed that many interesting and novel functionalized oligothiophenes have been synthesized by convenient coupling strategies (Heck, Kumada, Negishi, Suzuki, Stille and Ullmann) and oxidative coupling methods. Synthesis of polythiophenes are also presented and described according to chemical and electrochemical polymerization methodologies. The description of these noteworthy synthetic methods illustrates how important and promising are the interdisciplinary approaches in the obtaining of oligothiophenes and polythiophenes.

Um composto de fórmula [ttf]2[Cu(opba)]·H2O, com ttf = tetrathiafulvaleno e opba = orto-fenilenobis(oxamato), foi preparado e caracterizado. O complexo foi obtido por reação de metátese entre (ttf)3(BF4)2 e (Bu4N)2[Cu(opba)] em acetonitrila à temperatura ambiente. O espectro UV-Vis-NIR mostra a presença do radical cátion em duas formas, (ttf•+) e dímero (ttf•+)2. As propriedades de condutividade de [ttf]2[Cu(opba)]·H2O foram estudadas por espectroscopia de impedância (IS) e voltametria linear (LV) e mostram um comportamento típico de semicondutor. O espectro de EPR exibe duas linhas superpostas correspondentes aos spins eletrônicos de íons CuII e de radicais cátions ttf•+. As propriedades magnéticas (dc) mostram um valor do produto χMT na temperatura ambiente próximo ao esperado para três spins S = ½ desacoplados e um valor de 0.13 emu K mol-1 a baixas temperaturas (4 K). A curva do produto χMT versus T foi ajustada e o melhor modelo consiste de um termo para o dímero (ttf•+)2 (Bleaney-Bowers, resultando em J2 = -186 cm-1) e de um segundo termo relativo a uma cadeia antiferromagnética Cu···ttf •+ (J1 = -10.1 cm-1).

An oxamato-based compound of formula [ttf]2[Cu(opba)]·H2O, with ttf = tetrathiafulvalene and opba = ortho-phenylenebis(oxamato), has been prepared and characterized. The complex was obtained by metathesis from (ttf)3(BF4)2 and (Bu4N)2[Cu(opba)] in acetonitrile at room temperature. The UV-Vis-NIR spectrum reveals the presence of the radical cation in two forms, (ttf•+) and (ttf•+)2 dimer. The electronic transport properties of [ttf]2[Cu(opba)]·H2O were studied by impedance spectroscopy (IS) and linear voltammetry (LV), and show a typical semiconductor behavior. The EPR spectra exhibit two superposed lines corresponding to electron spins of CuII ions and ttf•+ radical cations. The dc magnetic properties show a room temperature value of the χMT product close to that expected for three uncoupled S = ½ spins and a value of 0.13 emu K mol-1 at low temperature (4 K). The χMT vs. T curve was fitted and the best model consists of a term for a (ttf•+)2 dimer (Bleaney-Bowers, leading to J2 = -186 cm-1) and a second term related to an antiferromagnetic {Cu···ttf•+} chain (J1 = -10.1 cm-1).

This paper is focused on a review of the design features and the electrochemistry characterization of anode-supported planar SOFC. Studies and results of metallic alloy interconnectors and recovery for protection against corrosion and for contact layer are showed. Moreover a discussion of examples of measurements of impedance spectrometry, according to the literature and our experimental results are made. For the anode supported fuel cells the power density varies from 0.1 to 0.5 Wcm², according to results in the literature (showed in this paper). For electrolyte supported fuel cell the power density can be 10 Wcm-2 for high temperatures. An English-Portuguese glossary of most used terms in SOFC stack is given for greater clarity and to introduce new terms to the reader.

A modelagem computacional contribui para o projeto, o dimensionamento e, também, para a avaliação do desempenho de pilhas a combustível de óxido sólido. No entanto, essa modelagem é complexa devido a grande quantidade de fenômenos físicos envolvidos. Além dos fenômenos físicos, as dimensões presentes dificultam a validação dos resultados. Neste trabalho, os canais de um interconector adjacente a um anodo foram modelados visando avaliar o escoamento nesse sistema. A validação dos procedimentos e das considerações foi feita de maneira indireta. O escoamento no interconector foi avaliado através das equações de Navier-Stokes e, no anodo, foi utilizada a Lei de Darcy. A técnica de volumes finitos foi empregada para a solução das equações. Foram utilizados valores típicos de permeabilidade, enquanto viscosidade e densidade foram determinadas numericamente, considerando a mistura de hidrogênio e água. Foi considerado regime permanente e isotropia em relação a todas as propriedades físicas determinadas a várias temperaturas. Foram analisadas as influências no escoamento da razão entre porosidade do anodo e viscosidade da mistura H2 e H2O; da densidade e; da temperatura. Um estudo de como a densidade da malha afeta os resultados também foi realizado. Foi possível notar que, quando a mistura hidrogênio/água penetra no meio poroso, o escoamento sofre uma redução de velocidade, em relação ao valor médio aplicado na entrada. Já a pressão, nessa situação, não apresenta redução significativa.

The computational modeling contribute for design, dimensioning and also for performance evaluation of Solid Oxide Fuel Cells. Nevertheless, the modeling is complex due to of large quantity of physics phenomena involved. In addition of physics phenomena, the present dimensions raise difficulties to validate the results. In this work, the interconnect channels adjacent to an anode have modeled aiming evaluate the flowing in this system. The validation of procedures and considerations has done by indirect mode. The flowing at interconnect has been evaluate through the Navier-Stokes equations and at anode it has been used the Darcy's Law. The technique of finite volume has used to solving of equations. It has been used typical values of permeability, while viscosity and density have been numerically determined, considering a mixture of hydrogen and water. It has been considered steady state and isotropy in relation of all physical properties determined at different temperatures. It have been analyzed the influences at the flowing by ratio between the porosity of anode and viscosity of mixture H2O and H2O; density and temperature. A study of how the mesh affects the results also has been done. It has been possible the see that, when the mixtures of hydrogen/water enters at porous media, the flowing suffer a reduction of velocity in relation of medium value applied at entering. The pressure, in this situation, does not show significant reduction.

Three compounds have been synthesized with formulae [3-MeRad][Ni(dmit)2] (1), [4-MeRad][Ni(dmit)2] (2) and [4-PrRad][Ni(dmit)2] (3) where [Ni(dmit)2]- is an anionic pi-radical (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) and [3-MeRad]+ is 3-N-methylpyridinium alpha-nitronyl nitroxide, [4-MeRad]+ is 4-N-methylpyridinium alpha-nitronyl nitroxide and [4-PrRad]+ is 4-N-propylpyridinium alpha-nitronyl nitroxide. The temperature-dependent magnetic susceptibility of 1 revealed that an antiferromagnetic interaction operates between the 3-MeRad+ radical cations with exchange coupling constants of J1 = - 1.72 cm-1 and antiferromagnetism assigned to the spin ladder chains of the Ni(dmit)2 radical anions. Compound 1 exhibits semiconducting behavior and 3 presents capacitor behavior in the temperature range studied (4 - 300 K).

The aim of this work is to present the theoretical and experimental aspects of the mirage effect technique. We are especially interested in the concentration mirage effect, which is a powerful tool in the study of electrochemical reactions that produce ionic movements close to electrodes and to get some fundamental information on mass transport and charge transfer during electrochemical processes. Limitations of this technique are discussed as well as the recent attempts to overcome them.

Estudamos o fenômeno de histerese inerente aos processos redox dos polímeros condutores eletrônicos (PCE). As histereses foram separadas em duas classes: i) as histereses dinâmicas constituídas por componentes cinéticas e ôhmicas e ii) as histereses estacionárias ou termodinâmicas. Efetuamos uma análise matemática das histereses dinâmicas observadas nos voltamogramas cíclicos de dois polímeros: a polianilina (PANI) e o poli(3-metiltiofeno) (P3MT). Mostrou-se que no caso do P3MT a histerese é principalmente cinética devido à velocidade de uma das etapas do processo redox com também uma componente ôhmica relacionada à existência de uma impedância elétrica em serie com o sistema eletroquímico. No caso da PANI, observou-se que a histerese é independe da corrente, o que é característico de uma histerese termodinâmica.

The hysteresis phenomenon inherent to redox processes of Electronic Conducting Polymers (ECP) has been studied. Hysteresis was divided into two classes: i) dynamic hysteresis, containing a kinetic and an ohmic component and ii) stationary or thermodynamic hysteresis. A mathematical analysis was performed on the dynamic hysteresis observed in cyclic voltammograms of two polymers: polyaniline (PANI) and poly(3-methylthiophene) (P3MT). It has been shown that in the case of P3MT, the hysteresis is mainly kinetic due to the rate of one of the steps of the redox process. However, an ohmic component related to the existence of an electrical impedance in series with the electrochemical system is also present. As for PANI, hysteresis is current independent, which is characteristic of thermodynamic hysteresis.