RCAAP Repository

Previous work by the authors has demonstrated a high rate and high yield hydrolysis of sodium borohydride in the presence of a Ni-Ru catalyst synthesized by wet chemistry. The catalyst has been fully characterized and utilized more than 300 times, exhibiting high stability and durability. In this work, the effect of temperature on the reaction rate was studied and the activation energy of the process estimated for temperatures up to 65 ºC. Typical data in the form of an Arrhenius type relationship showed two slope regions suggesting a change of mechanism that lead to a more accentuated role of ruthenium for temperatures higher than 45 ºC. This effect is maintained with increasing Ru doping of the catalyst. The effect of NaOH as a stabilizer was also studied and the role of Ni and Ru in the hydrolysis of sodium borohydride is under study on the basis of data obtained for various Ru concentrations and data for 100% Ni and 100% Ru as catalysts. An increase in the concentration of Ruthenium in the catalyst allowed effective utilization of the catalyst without the need for the stabilizer, minimizing the induction reaction time. Excellent catalytic activity and catalyst minimal deactivation for sodium borohydride hydrolysis are characteristic of the series of Ni-Ru catalyst synthesized by wet chemistry used in this work.

The LaNiO3 perovskite-type oxide is one of the most tested anode for the oxygen evolution reaction in alkaline solutions. It is well established that the oxide preparation conditions and the electrode fabrication are key factors to control the electrochemical behaviour of oxide coatings. In a previous work the authors studied the influence of preparation conditions of the oxide and support type on the electrochemical behaviour of Ni foam coated LaNiO3 electrodes. Ni foam was selected as support due to its unique characteristics namely low contact resistance between the oxide and support, possibility of high metal oxide loadings and dimensional stability [1]. No studies were performed, concerning the influence of the oxide loading. Studies performed by Singh et al. on LaNiO3 coatings on Ni foil supports have shown that the electrode roughness factor increased with increase in oxide loading at the beginning and finally attained a constant value around 0.03 g cm-2 [2]. The present work reports on the study of the dependence of roughness factor (Rf) and morphology factor (φ) on the oxide loading for Ni foam coated LaNiO3 electrodes with loadings varying between 0.02 and 0.14 g cm-2. Cyclic voltammetry and electrochemical impedance spectroscopy were used to evaluate the Rf and φ values, complemented by optical microscopy observations. A non-linear increase of both Rf and φ with the oxide loading is observed, showing a level off when the oxide loading is increased. The level off was interpreted as a progressive exclusion of the crystallites from the contact with the solution as the oxide coating thickness increases.

The mechanisms of fuel cell degradation are multiple and not well understood. Irreversible changes in the kinetic and/or transport properties of the cell are fostered by thermal, chemical and mechanical issues which constrain stability, power and fuel cell lifetime. Within the in-situ diagnostics methods and tools available, in-situ electrochemical impedance spectroscopy (EIS) is within the most promising to better understand and categorize changes during fuel cell ageing. In this work, the degradation phenomena caused by cell polarity reversal due to fuel starvation of an open cathode 16 MEA (membrane-electrode assembly) –low power PEM fuel cell (15 W nominal power) is reported using EIS as a base technique. A frequency response analyzer from Solartron Model 1250 was used connected to an electrochemical interface also from Solartron, Model 1286. The range of covered frequencies spans from 37000 Hz to 0.01Hz. Hydrogen is supplied from a metallic hydride small reactor with a capacity of 50 NL H2 at a pressure of 0.2 bar. Measuring the potential of individual cells, while the fuel cell is on load, was found instrumental in assessing the “state of health” of cells at fixed current. Location of affected cells, those farthest away from hydrogen entry in the stack, was revealed by the very low or even negative potential values. EIS spectra were taken at selected break-in periods during fuel cell functioning. The analysis of impedance data is made using two different approaches: using an a priori equivalent circuit describing the transfer function of the system in question -equivalent circuit elements were evaluated by a complex non-linear least square (CNLS) fitting algorithm, and by calculating and analyzing the corresponding distribution of relaxation times (DRT) -avoiding the ambiguity of the a priori equivalent circuit and the need for provision of the initial fitting parameters. A resistance and two RQ elements connected in series are identified as describing the impedance response of the cell during normal functioning. A constant phase element (CPE) was chosen to describe the impedance observed behavior. The quality of the fit was evaluated by analysis of the residuals between the fit result and the measured data at every single point. Consistency and quality of the impedance data were established by Kramers-Kronning validation. With continuous operation, using a reduced hydrogen flow, an inversion of polarity was observed in the 16th cell of the stack, evident in the potential measurement of individual cells as a result of insufficient hydrogen to reach the last cells. EIS data analyses suggest that water electrolysis happens at the anode judging by the appearance of an intermediate semicircle associated to a marked change in resistance and capacitance values. The presence of an inductive loop at low frequencies is now evident, which cannot be explained by the relaxation of reaction intermediates involved in the oxygen reduction reaction [1]. It is to be noticed that when the incursion into the negative potential values is not too marked the phenomenon is partially reversible, so it is suggested that the relaxation is due to intermediates in the water electrolysis process. The anode potential rose to levels compatible with the oxidation of water. Once the phenomenon is made irreversible and when water is no longer available, oxidation of the carbon support is favored accelerating catalyst sintering. Ex-situ MEA cross section analysis, under a scanning electron microscope, confirmed it. Electrode thickness reduction and delamination of catalyst layers were observed as a result of reactions taking place during hydrogen starvation. Carbon corrosion and membrane degradation are analyzed, according to evidence by SEM.

Previous work by the authors has demonstrated a high rate and high yield hydrolysis of sodium borohydride, in the presence of a Ni-Ru catalyst synthesized by wet chemistry. The catalyst has been fully characterized and utilized more than 300 times exhibiting high stability and durability. In this work, results of an electrochemical study are reported using the powder catalyst supported on a Ni foam in order to measure the open circuit potential during hydrogen production and to study the reaction using voltammetry and ac impedance. Production rates were as high as 10 Lmin-1gcat -1 at 65ºC. Electrochemical studies indicated that the hydrogen evolution mechanism corresponds to a Volmer- Heyrovsky type, suggested by a Tafel slope of 117 mVdec-1. Tafel region potentials are in agreement with values found for hydrolysis at the open circuit. The Langmuir-Hinshelwood mechanism explains the hydrolysis of sodium borohydride using a Ni-Ru catalyst. The role of Ni and Ru is briefly discussed.

O presente trabalho investiga de que forma a literatura infantil contribui para uma aprendizagem crítico reflexiva, baseada no desenvolvimento da autonomia e da criatividade dos estudantes, com intuito de mobilizar os alunos do ensino fundamental em prol da melhoria do processo de leitura, tentando verificar se o mesmo se assume como inovação pedagógica. O estudo foi desenvolvido através do tema: “A literatura infantil nas escolas do campo brasileiras e a inovação pedagógica: um estudo de práticas pedagógicas nas séries iniciais do ensino fundamental”. O campo de pesquisa foi uma Escola Pública Rural do Município de Poção – Pernambuco, Brasil, que trabalha com a literatura infantil na sala de aula e teve como sujeitos estudados, os alunos do 5º ano do Ensino Fundamental, a professora e a gestão da escola. A metodologia desenvolvida é de um estudo de caso de natureza qualitativa que adota a observação participante, com notas de campo como procedimento principal de coleta de dados, bem como a entrevista semiestruturada e a recolha de documentos. Assim, a presente investigação insere-se numa abordagem qualitativa dos fenômenos educativos que teve como resultados a evidência que a literatura infantil pode ser considerada uma ferramenta significativa para o processo de ensino-aprendizagem bem como para motivar o gosto pela leitura e garantir uma formação cultural e cidadã. Portanto, a prática educativa através da literatura infantil manifesta traços de inovação pedagógica e a postura dos professores e alunos tem demonstrado práticas pedagógicas inovadoras, uma vez que proporcionam uma aprendizagem crítico reflexiva, baseada no desenvolvimento da autonomia e da criatividade dos estudantes.

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Dissertação com o tema Hipertexto e Gêneros Digitais: Práticas Pedagógicas Inovadoras no Ensino Médio? Que se propôs a compreender até onde as práticas com o gênero textual hipertexto contribuem para uma aprendizagem fundamentada no desenvolvimento da criticidade, criatividade e autonomia dos discentes. Arguindo se o trabalho com esse gênero no ensino médio, desperta o desenvolvimento crítico da autonomia e interação sociocultural podendo ser considerado uma prática inovadora. Enfatizaram-se as categorias Hipertexto e Gêneros Digitais e Inovação pedagógica. A pesquisa foi realizada através de estudo de caso com abordagem qualitativa utilizando como procedimentos metodológicos entrevistas, revisão bibliográfica e observação participante. O caminhar investigativo permitiu observar que as produções dos aprendizes apresentavam aspectos importantes em relação a edificação do saber pelos discentes, uma vez que eles eram autônomos em relação a aquisição de conhecimento e se mostravam ativos em relação a execução das atividades propostas com o hipertexto. Aguçavam suas percepções e demonstravam melhorias nas linguagens escrita e oral, bem como no relacionamento entre os pares e com a sociedade ao seu redor. Durante este percurso constatamos ainda o quanto as mudanças nas posturas pedagógicas do docente, associadas à um local de estudo que difere dos padrões de uma sala de aula tradicional, podem contribuir para aumentar a motivação, a cooperação, a autoestima e a autonomia dos aprendizes. Podemos concluir mencionando que a influência positiva do ambiente no qual se desenvolvem as atividades, uma vez que nesse espaço os aprendizes se mostraram motivados à produzirem e compartilharem conhecimentos.

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Electrochemical sensors are devices that allow the detection and quantification of a certain compound in a determined sample. Nanomaterials are extremely appealing for sensing purposes due their properties. Poly(amidoamine) dendrimers and gold nanoparticles are largely explored because of their small dimensions; the latter is used for its electrocatalytic properties, whilst the former is used in biosensors for its potential as an immobilization platform for biological recognition elements. This project focused on the use of PAMAM dendrimers and gold nanoparticles in electrode modification and the assessment of these modifications. Firstly, gold and glassy carbon electrodes were sequentially modified with thiols, gold layer, G5 PAMAM-NH2 dendrimers and citrate-stabilized gold nanoparticles. The modifications were monitored by cyclic voltammetry and impedance spectroscopy in a hexacyanoferrate (II)/(III) redox couple system. All modifications were successful, with the exception of citrate-stabilized gold nanoparticle, PAMAM dendrimer and mercaptopropionic sulfonic acid modified glassy carbon electrode. In a second part, the electrocatalytic activity of the modified electrodes towards 4-nitrophenol reduction in 0.05 M phosphate buffer solution was assessed by cyclic voltammetry. G5 PAMAM NH2 dendrimer assembly over vitreous carbon-based surfaces translated to electrodes with higher sensitivity, for lower limits of detection are obtained. The lowest limit of detection was calculated for PAMAM dendrimer and 3mercaptopropionic acid-modified glassy carbon electrode, 17 M, with 4-nitrophenol in linear range of 690 – 37 M. Gold substrates proved to have poor electrocatalytic activity towards 4-nitrophenol reduction owing to the simultaneous reduction of 4-nitrophenol and solution on gold surface. As for vitreous carbon substrates, the use of gold, either as a layer or as citrate-stabilized nanoparticles, resulted in less sensitive electrodes, as suggested by higher detection limits.

Este artigo apresenta o projecto DROIDE VIRTUAL, que tem por objectivo descrever, analisar e compreender o processo de construção do conhecimento sobre conceitos de programação e o desenvolvimento de competências nesta área. O projecto tem uma duração de três anos ― sendo este o primeiro ano ― e envolve estudantes do ensino secundário da Madeira, Açores, Canárias e Cabo Verde, os quais aprendem programação desenvolvendo pequenos projectos de robótica através da colaboração virtual em um ambiente de aprendizagem baseado na web.

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A água é um recurso essencial para a nossa sobrevivência, mas é cada vez mais escassa. Estima-se que daqui a 32 anos não existirão reservas suficientes de água para a produção alimentar. Este projeto tem como objetivo o desenvolvimento de um sistema que permita consciencializar as pessoas para uma redução do consumo de água. Tendo esse objetivo em vista, desenvolveu-se um sistema que inclui sensores e atuadores dispersos pela rede de águas. Os sensores permitem a recolha de dados do consumo de água, da temperatura e da pressão. No que toca aos atuadores, estes permitem o controlo/corte de água. Toda a informação recolhida é armazenada numa base de dados. O sistema tem ao seu dispor vários meios para a promoção da consciencialização do utilizador. Em primeiro lugar, possui uma aplicação móvel que permite ao utilizador estar ao corrente dos seus consumos. Em segundo lugar, conta com um website que tem como objetivo ilustrar os consumos do utilizador. Em terceiro lugar, usufrui de um assistente virtual que permite ao utilizador estar ao corrente dos seus consumos, controlar a rede de água por comandos de voz e auxiliá-lo nas tarefas diárias relacionadas com a água. O auxílio nas tarefas diárias permite a promoção de um comportamento responsável no consumo de água. Um exemplo desse auxílio é o ajudar na tarefa da lavagem dos dentes, em que o assistente ao longo da tarefa vai mantendo o utilizador ao corrente do tempo decorrido e controla a rotina de abertura e fecho da torneira. Neste projeto implementou-se o sistema em 3 casas e um edifício. Estas implementações permitiram avaliar o funcionamento do sistema e a recolha de consumo de diversos utilizadores. Avaliando os dados recolhidos, estes permitiram a deteção de padrões de consumo nas rotinas de tomar duche, lavar os dentes e a recarga do autoclismo.

Hexa- and nonanitrile ligands were synthesized by the known CpFe+-induced hexaallylation of hexamethylbenzene in [FeCp(η6-C6Me6)][PF6] and nonaallylation of mesitylene in [FeCp(η6-1,3,5-C6H3Me3)][PF6], respectively, followed by Pt-catalyzed regioselective hydrosilylation of the iron-free polyolefins using (chloromethyl)dimethylsilane and sodium iodide catalyzed Williamson coupling with p-hydroxybenzonitrile. The hexanitrile star was coordinated to the piano-stool ruthenium complex [RuCp(PPh3)2Cl] by substitution of the six ruthenium-bound chlorides with nitriles using TlPF6 to give the hexacationic hexaruthenium star complex, whereas the analogous metalation reaction partly failed, due to bulk constraint with the nonanitrile ligand. The strategy that involved lengthening of the tethers of the latter, however, successfully provided a nonacationic nonaruthenium complex.

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Large scale wind power production and its variability is one of the major inputs to wind integration studies. This paper analyses measured data from large scale wind power production. Comparisons of variability are made across several variables: time scale (10-60 minute ramp rates),number of wind farms, and simulated vs. modeled data. Ramp rates for Wind power production, Load (total system load) and Net load (load minus wind power production) demonstrate how wind power increases the net load variability. Wind power will also change the timing of daily ramps.

The Power Systems in Denmark, Portugal, Spain, Ireland, and Germany have some of the highest wind penetrations in the world, as shown in Table 1. The management of the different power systems to date,with increasing amounts of wind energy, has been successful.There have been no reported incidents in which wind has directly or indirectly been a major factor causing operational problems on the system. In some areas with high wind penetration, however, the transmission system operator (TSO) had to increase remedial actions signifi cantly in order to decrease the loading of system assets during times of high wind power infeed. In some areas, the risk of faults may have increased. Higher targets for wind power will mean even higher penetration levels locally and high penetration levels in larger power systems. There are a number of issues that will require active management in the near future; in some cases, such management is needed today. In this article, the situations of five countries with high wind penetration are briefl y presented, with special emphasis given to their future needs with respect to accommodating targeted wind power amounts. The final section provides an overview of offshore grid developments and plans in Europe.

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O elevado consumo de energia nos edifícios tem vindo a ser responsável pela publicação de legislação europeia que visa limitar esse consumo, por via da melhoria dos processos construtivos e da adopção de estratégias de redução do consumo em paralelo com a definição de esquemas de certificação energética que permitam ao mercado escolher e por essa via promover a disseminação das melhores práticas. Em Portugal é o RCCTE, actualmente em processo de revisão, que para além dos requisitos mínimos construtivos obriga a colocação de colectores solares térmicos, mas também valoriza a introdução de outras renováveis nos edifícios. Neste texto iremos percorrer de forma sucinta, as várias tecnologias e aspectos de desenho que já se apresentam no terreno ou se perfilam no horizonte próximo e que em conjunto permitem aproximar de zero, o balanço energético dos edifícios.

A research work has being carried out aiming at evaluating the possibility of treating simultaneously several electrochemical systems of spent batteries using the same process, in order to overcome the high costs and difficulties of selective collection and sorting. Zn-MnO2 systems, representing more than 75% of portable battery market, shall be treated in dedicated processes. The treatment assessment using a single hydrometallurgical process of the other major systems (NiCd, NiMH and Li-ion), having Ni and Co as main metals, was the aim of the research work here reported. Sulfuric acid leaching was demonstrated to be adequate for dissolving more than 90% of the metals of interest contained in batteries. The subsequent separation of metals by solvent extraction, using organophosphorous extractants like DEHPA and Cyanex 272, allowed the production of pure solutions of rare earths, cadmium/manganese, cobalt, nickel and lithium, enabling their further recovering

International scientific mobility is a strategic element in the science policies of several countries, being often equated with the development of extensive knowledge networks that can be mobilised by the scientists (and their organisations) upon their return. The objective of this paper is to understand whether and in which conditions mobility leads to the development of knowledge links that are long lasting and effectively play a key role in scientists’ activities. In conceptual terms, the influence of mobility is explained through the opportunities it provides for temporary co-location in one organisation, and thus for the creation of social, cognitive and organisational proximity between scientists, which are critical for knowledge transmission and which can persist after the individuals draw apart. This conceptual framework supports an empirical analysis of the impact of two types of long term mobility - for training and professional purposes - on the creation of “persistent knowledge networks”, in the case of Portuguese scientists. The results show that mobile scientists are more likely to have foreign organisations in their core knowledge network. Even more importantly, they reveal a high incidence of organisations that were part of the scientists’ trajectory in these networks, providing some confirmation to the effects of colocation. However, these effects are not always present: the research also identifies some factors – related with personal characteristics, career situation, scientific field, time, geographical distance, motivations to move - that increase the likelihood of network persistence, which differ for the two types of mobility.