ME - Resumos em livros de actas
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- AA 5083 aluminium alloy corrosion in estuarine environmentPublication . Marques, Maria João; Alves, Isabel Nascimento; Gonçalves, Rita
- Advances in electrochemical reduction of CO2 in ionic liquid-based electrolytes [Resumo]Publication . Machado, Ana; Messias, Sofia; Paninho, A. B.; Nunes, A. V. M.; Rangel, C. M.; Branco, Luis CABSTRACT: Electrochemical reduction of CO2 was for the first time reported in 1870 [1], but it was only after 2010 that this field was the subject of intense research efforts. The use of renewable electricity to convert CO2 into products that are currently derived from fossil products and have high carbon footprint will certainly make this technology one pillar of a sustainable chemical industry. The scepticism towards the availability of cost effective products derived from CO2 electro-reduction that customers will be willing to buy has shifted to the belief that they can be commercially viable. Turning electrochemical CO2 reduction into a commercial technology will depend on economics, on the price of electricity, efficiency of the process and the value of the products. One way to improve the economics and improve the efficiency of the process is to integrate CO2 capture with conversion [2,3]. In this way the energy intensive regeneration step of the capture media can be eliminated and also CO2 transportation and storage. Ionic liquids are ideal media to achieve this integration, due to high CO2 adsorption capacity, high selectivity, wide electrochemical windows and nearly zero vapour pressure. The present work reports the progress of electrochemical reduction of CO2 in ionic liquids and the work of the authors in this field. It has been recognized that ionic liquids promote CO2 electro-reduction through lowering the reduction potential, the suppression of the competing hydrogen evolution reaction and by increasing the selectivity towards the target products. However, the understanding of the interactions between ionic liquids, CO2 and catalyst is still quite limited, but fundamental for synthetizing more efficient electrolytes for CO2 electro-reduction [4]. Thus, current cation and anion effects will be analysed and an overview of the current performance of heterogeneous electro-catalysts in ionic liquid- based electrolytes for CO2 electro-reduction will be provided.
- Alternative baths for the gold electrodeposition based on 1-butyl-1-methyl-pyrrolidinium dicyanamide ionic liquidPublication . Sá, A.I. De; Quaresma, S.; Eugénio, S.; Rangel, C. M.; Vilar, R.
- Aluminium en milieu marin : protection par la biocorrosion [Resumo]Publication . Jaume, Julien; Basseguy, Regine; Marques, Maria João; Délia, Marie-LineABSTRACT: Pour être utilisés en milieu marin, les matériaux doivent être particulièrement résistant à la corrosion, du fait de la composition chimique de l’eau de mer (concentration en chlorure élévée, …) mais également de la présence des microorganismes. En effet, les microorganismes sont connus pour catalyser la corrosion ou l’inhiber [1,2]. Ces phénomènes antagonistes sont regroupés sous le terme de « Microbiologically Influenced Corrosion » (MIC) et « MIC Inhibition » (MICI). Les alliages d’aluminium Al-Mg, série 5000 qui présentent une bonne résistance mécanique mais également à la corrosion, sont un matériau de choix pour les structures immergées dans l’eau de mer.
- An electrochemical process for the production of synthetic fuels at low temperatures [Resumo]Publication . Fernandes, Vitor; Furtado, Olívia; Rodrigues, J.; Rangel, C. M.Following work exploring the low temperature electrolysis in alkaline media, using graphite consumable anodes, from which syngas was obtained1, laboratory studies have been conducted in acid media pursuing higher efficiency in the production of hydrogen and synthetic fuels. Experiments were conducted in an own designed undivided planar cell with 25 cm2 geometrical area electrodes using a 0.5 M H2SO4 solution with and without Fe(II) additions. Fe2+ oxidizes to Fe3+ at the anode surface. The redox couple Fe3+/ Fe2+ acts as an oxidation mediator not only oxidizing the bulk and detached graphite but also the surface functional groups. The practical experimental potential for graphite oxidation is within the range for the electroxidation of the Fe redox couple giving as a result a 4-fold increase in the amount of produced CO2 at near room temperature, when using 0.025 M FeSO4.
- Assessing cell polarity reversal degradation phenomena in PEM Fuel Cells by electrochemical impedance spectroscopyPublication . Travassos, Maria Antónia; Lopes, Vitor V.; Novais, Augusto Q.; Rangel, C. M.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.
- Assessing performance and degradation in PEM Fuel Cells by electrochemical impedancePublication . Rangel, C. M.; Silva, R. A.; Paiva Luís, Teresa
- Assessing performance and degradation mechanisms in proton exchange membrane Fuel CellsPublication . Rangel, C. M.; Silva, R. A.; Paiva Luís, Teresa
- Autonomous hydrogen systems: control strategyPublication . Martins, João F.; Viana, Susana; Joyce, A; Pires, Armando; Rangel, C. M.; Sotomayor, João; Castro, RuiThis paper describes the control strategy for a Stand-Alone Energy System Supported by Totally Renewable Hydrogen Production. The basic control strategy considers the pressurized hydrogen gas storage as the energy buffer. The basic logic is that the exceeding renewable energy (solar and wind) is used to accumulate hydrogen, while the fuel cell uses this hydrogen to produce electrical energy within insufficient solar/wind energy. The system is completely autonomous, conceived for off-grid operation. It is composed by solar panels and a wind turbine as primary energy converters, hydrogen tanks as energy buffer and a fuel-cell and an electrolyzer as secondary energy converters.
- Bisfosfonatos derivados do indazole: síntese e avaliação da actividade biológicaPublication . Matias, G.; Teixeira, Fatima; Martins, M. R.; Caldeira, A. T.; Teixeira, António P. S.