Pyrite Photoanode/Redox Electrolyte Interface: Characterization of the Interaction of the Reducing Species with Pyrite Through Temperature Dependence Measurements

At the semiconductor pyrite photoanode/electrolyte interface, the interaction of the reducing species containing-electrolyte was investigated by temperature dependence measurements. An increase of negative entropy turnover could be related to negatively charged species interacting with the positively charged pyrite surface. Further studies, using the impedance technique in darkness and under illumination, showed that kinetic and diffusion- -like processes control this interface. In the determination of the activation energy both dc and ac techniques lead to compatible results

Chalcogenides and Carbon Nanostructures: Great Applications for PEM Fuel Cells

Nanostructured metal chalcogenides (NMCs) and carbon nanostructures (CNS) are attracting significant attention due to their features such as high stability in an acidic environment, especially if they have a significant oxygen reduction activity and remarkable superconducting properties. The broad range of CNS exhibits novel physicochemical properties, and thus it is triggering intense research about carbon nanoscience with numerous applications. In this context, new synthesis routes are designed under moderate conditions, which are definitely needed in order to simplify the process, reduce costs, and allow the production of NMCs at lower temperatures and CNS whose size and shape can be controlled. Some related studies about Pt based on sulfides and selenides, transition metal chalcogenides (TMCs), and carbon nanostructures (nanotubes and graphene) are revealed here; however, they show promise for fuel cells that these NMCs, CNS, or even NMC-CNS materials have been applied for other energy devices. Until now, a good response for cathodic reactions is employing TMCs based on tungsten and CNS without metal. According to experimental results and in terms of catalytic activity, durability, and chemical/electrochemical stability, much more research is required to produce commercially valid non-noble catalysts, electrocatalysts, or supports; however, one approach on this field is metal-free CNS

Développement de catalyseurs cathodiques nanométriques sélectifs à l'environnement organique pour leur utilisation dans une pile microfluidique

Les piles à combustible sans membrane polymérique comme les piles à combustible microfluidique ont des perspectives très intéressantes pour des applications énergétiques à basse puissance. L'étude menée consistait donc à poursuivre le développement de catalyseurs cathodiques nanométriques pouvant être utilisés en tant que cathode dans une pile à combustible microfluidique directe. Au cours de ce travail de thèse, une modification du comportement catalytique du platine a été réalisée grâce à un effet de support, d'alliage avec un métal de transition 3d (titane), ou bien encore par coordination de la surface de nanoparticules de platine avec un élément chalcogène (sélénium). Les effets induits par ces modifications sur les propriétés électroniques du matériau catalytique, et leurs implications sur son activité catalytique ont été étudiés au même titre que sa stabilité et sa tolérance vis-à-vis de petites molécules organiques. Les études ont été menées dans le but de présenter un nouveau paradigme des relations structure-activité, structure-stabilité et structure-tolérance gouvernant le comportement catalytique d'une surface de platine. Les expériences ont par voie de conséquence été conduites de façon à pouvoir séparer les effets catalytiques induits par le support, de ceux induits par un effet d'alliage ou bien encore par coordination des atomes de surface avec un élément chalcogène. En conclusion, ces études ont démontrés l'effet de l'interaction du métal avec le support (oxyde ou matériau carboné présentant divers degrés de graphitisation) sur l'activité et la stabilité des catalyseurs. Un autre point important, qui a été développé dans ce travail de thèse, est la modifFuel cells without polymeric membrane such as the microfluidic fuel cells (MFFC) possess very interesting perspectives for low-power energy applications. The study aimed at pursuing the development of nanometric cathodic catalysts and to study their activity, stability and tolerance in a microfluidic system. In the present thesis, the activity, stability and tolerance of Pt-based nanoparticle electrocatalysts were investigated. The effect of the support materials and the influence of surface modification by a second element including 3d transition metal (titanium) and chalcogenide (selenium) were studied. The separation and reduction of the complexity of the interaction between nanoparticles-support and nanoparticles modification by a second element enables to achieve a clear relationship of the structure-activity-stability-tolerance of the supported fuel-cell electrocatalysts. The present experimental results from the effects of the support materials and of the modification of Pt by a second element led to improve activity, stability and tolerance. The developed approach and acquired knowledge about surface property correlation can be further generalized and used in the design of advanced selective electrocatalysts. Furthermore, the synthesized electrocatalysts were used as cathode in an organic microfluidic fuel cell.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

Electrochemical impedance spectroscopy of dodecylsulphate doped polypyrrole films in the dark and under illumination

The morphology, thickness, oxidation and illumination effects in dodecylsulphate doped polypyrrole films can be qualitatively observed by EIS and consist in variations of interfacial and bulk resistances and capacitances of a proposed equivalent circuit. The circuit well with the measured spectra of films obtained with 190 mC cm-2 of synthesis charge density. For thinner films the calculated values observed by electrochemical impedance spectroscopy (EIS) deviate probably due to the absence of diffusion effects. The oxidation of the films diminishes the total impedance over the entire frequency range. The morphology effects are also observed in the entire spectra. The illumination effects are reversible and are observed as expected only in the reduced form of the polymer. The illumination reduces the internal resistance and the space-charge capacitance and increases the charge transfer resistance and the double layer capacitance.Efeitos de morfologia, espessura, oxidação e iluminação dos filmes de polipirrol dopados com dodecilsulfato podem ser observados qualitativamente por EIS e consistem de variações de valores de resistências e capacitâncias de um circuito equivalente proposto, presentes nas interfaces e no interior do material. O circuito se ajusta bem para filmes sintetizados com densidade de carga de 190 mC cm-2. Para filmes mais finos os valores calculados por espectroscopia de impedância eletroquímica (EIS) apresentam desvios provavelmente pela ausência de efeitos difusivos. A oxidação dos filmes causa uma diminuição geral da impedância em toda a faixa de freqüências medidas. Os efeitos de morfologia também são observados em todas as freqüências. Os efeitos de iluminação são reversíveis e aparecem, como esperado, apenas quando o polímero está na forma reduzida. A iluminação diminui a resistência interna e a capacitância de carga espacial e aumenta a resistência de transferência de carga e a capacitância de dupla camada.5058Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Structuring Porous Iron-Nitrogen-Doped Carbon in a Core/Shell Geometry for the Oxygen Reduction Reaction

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Water-splitting electrocatalysis in acid conditions using ruthenate-iridate pyrochlores

The pyrochlore solid solution (Na0.33Ce0.67)(2)-(Ir1-xRux)(2)O-7 (0<x<1), containing B-site Ru-IV and Ir-IV is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru, Ir)O-2 catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L-III and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in + 6 or higher oxidation states

Insetos Aquáticos Associados a Macrófitas Submersas com Diferentes Complexidades Morfológicas

The aim of the study was to analyze the diversity and community structure of aquatic insects associated with species of submersed macrophytes with different morphological complexity in relation to leaf structure. Sampling occurred in raining and dry periods at Ribeirão das Anhumas, Américo Brasiliense/SP. Four macrophytes were analyzed: Vallisneria sp., Eleocharis sp., Egeria najas and Ottelia sp. The entomological community was identified up to the family level, and at tribe level for Chironomidae. The community structure was analyzed using diversity indices of Simpson, Equitability evenness, relative participation of functional category and taxa dominance. The dispersion of faunal composition between the different collection periods was analyzed using a n-MDS with Morisita index. The structure of the insect community associated with macrophytes with different structural morphologies was analyzed using structural similarity calculated by the Bray-Curtis index. Seventeen families were identified from five orders, a total of 1642 specimens. The family Hydropsychidae (Trichoptera) presented eudominance (52.6%), followed by the tribe Pentaneurini (Chironomidae) (13.8%) and family Trichoryithidae (Ephemeroptera) (10%). The results showed that there were no large diversity variations in the analyzed macrophyte species and the sampling periods. The predator and collector functional groups were predominant. The n-MDS analysis indicated the absence of seasonal variation and, the similarity analysis indicated that macrophyte E. najas and Otellia sp., presented similar fauna structure, differing from other analyzed species. The results demonstrated that the morphological structure of macrophytes may have different structures of aquatic insect communities.O objetivo deste estudo foi analisar a diversidade e a estrutura da comunidade de insetos aquáticos associadas à macrófitas aquáticas submersas com diferentes complexidades morfológicas com relação às estruturas foliares. As coletas ocorreram em períodos seco e chuvoso, no Ribeirão das Anhumas, Américo Brasiliense/SP. Foram analisadas quatro espécies de macrófitas submersas: Vallisneria sp., Eleocharis sp., Egeria najas e Ottelia sp. A entomofauna coletada foi identificada até o nível de família, com exceção de Chironomidae, identificada até nível de tribo. A estrutura da comunidade foi analisada através dos índices de diversidade de Simpson, Equitabilidade de Pielou, participação relativa de categoria funcional e dominância de táxons. A composição faunística entre os diferentes períodos de coleta foi analisada por meio de uma n-MDS com índice de Morisita. A estrutura da comunidade de insetos associada a macrófitas, com diferentes morfologias estruturais, foi analisada por meio da similaridade, calculada pelo índice de Bray-Curtis. Foram identificadas 17 famílias pertencentes a cinco ordens, de um total de 1642 espécimes. A família Hydropsychidae (Trichoptera) apresentou eudominância (52,6%), seguidas pela tribo Pentaneurini (Chironomidae) (13,8%) e da família Trichoryithidae (Ephemeroptera) (10%). Os resultados demonstram que não houve grandes variações da diversidade entre as espécies de macrófitas analisadas e períodos de coleta. Os grupos funcionais predadores e coletores foram predominantes. A análise de n-MDS indicou ausência de variação entre os períodos de coleta. A análise de similaridade indicou que as macrófitas E. najas e Otellia sp. possuem estrutura faunística similar, diferenciando-se das demais espécies analisadas. Os resultados demonstraram que a estrutura morfológica das macrófitas pode apresentar distintas estruturas de comunidades de insetos aquáticos

What difference does a thiophene make? Evaluation of a 4,4′-bis(thiophene) functionalised 2,2′-bipyridyl copper(I) complex in a dye-sensitized solar cell

AbstractThe synthesis of a 4,4′-bis(2-thienyl-5-carboxylic acid) functionalised 2,2′-bipyridine ligand and corresponding copper(I) complex is described and its application in a dye-sensitized solar cell (DSSC) is studied. The positioning of the thiophene groups appears favourable from DFT analysis and a best efficiency of 1.41% was obtained with this dye, for a 0.3 cm2 cell area DSSC. Two absorbance bands are observed in the electronic absorption spectrum of the copper(I) complex at 316 nm and 506 nm, with ε values of 50,000 M−1 cm−1 and 9030 M−1 cm−1, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy are also used to provide a detailed analysis of the dye and assess its functionality in a DSSC

Pt-Sn/C as a possible methanol-tolerant cathode catalyst for DMFC

An effective method was developed for preparing highly dispersed nano-sized Pt–Sn/C electrocatalyst synthesised by a modified polyol reduction method. From XRD patterns, the Pt–Sn/C peaks shifted slightly to lower 2θ angles when compared with commercial Pt/C catalyst, suggesting that Sn formed alloy with Pt. Based on HR-TEM images, the Pt–Sn/C nanoparticles showed small particle sizes and well dispersed onto the carbon support with a narrow particle distribution. The methanol oxidation reaction on the as-prepared Pt–Sn/C catalyst appeared at lower currents (+7.08 mA at +480 mV vs. Ag/AgCl) compared to the commercial Pt/C (+8.25 mA at +480 mV vs. Ag/AgCl) suggesting that the Pt–Sn/C catalyst has ‘methanol tolerance capabilities’. Pt–Sn/C HA Slurry pH3 catalysts showed better activity towards the oxygen-reduction reaction (ORR) than commercial Pt/C which could be attributed to smaller particle sizes. In our study, the Pt–Sn/C catalyst appears to be a promising methanol-tolerant catalyst with activity towards the ORR in the DMFC.Web of Scienc