XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

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XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society K N 05 Electrochemical degradation of organic pollutants: optimization of the experimental conditions Ana Lopes UMTP and Department of Chemistry, University of Beira Interior, 6201-001 Covilhã, Portugal analopes@ubi.pt Biological degradation is the cheapest process for removal of organic pollutants from wastewaters. However, some compounds have low biodegradability or give origin to biotic products that persist in the receiving waters. When conventional biological treatments fail, a tertiary process, like chemical or electrochemical coagulation, adsorption or membrane filtration, is usually performed, with the disadvantage of sludge formation. Other alternatives, such as chemical oxidation with strong oxidants and advanced oxidation processes, besides being quite expensive, still present operational problems. Anodic oxidation techniques have also shown to be very efficient in the degradation of organic persistent pollutants. The use of these processes in wastewaters treatment has been intensively investigated in the last two decades [1,2]. The materials that can be used as electrodes are numerous and some of them are extraordinary promising. In particular, boron doped diamond (BDD) anodes have received great attention in the last years, due to their unique characteristics of mechanical and electrochemical stability, wide potential window for oxygen evolution and ability to produce radical species capable of oxidation of most of the organic pollutants [2-7]. Although anodic oxidation with BDD electrodes can be very effective, energetic costs are a drawback in the application of these techniques at industrial scale. This way, the optimization of experimental parameters and hydrodynamic conditions, in order to reduce maintenance costs, are a requirement for the implementation of these processes. In this study, the influence of pollutant type and concentration, electrolyte concentration, initial pH, applied current density, operation mode, stirring speed and recirculation flow rate in the organic load removal are evaluated. Acknowledgments: The financial support of Fundação para a Ciência e a Tecnologia, F CT, PDCT/AMB/59392/2004, PDCT/AMB/59388/2004, PTDC/CTM/64856/2006 and PTDC/AAC- AMB/103112/2008 and Adamant Technologies are gratefully acknowledged. References [1] Juttner, K., Galla, U., Schmieder, H., Electrochim. Acta, 2000, 45, 2575. [2] Martínez-Huitle, C.A., Ferro, S., Chem. Soc. Rev., 2006, 35, 1324. [3] Morão, A., Lopes, A., Pessoa de Amorim, M.T.,.Gonçalves, I., Electrochim. Acta, 2004, 49, 1587. [4] Panizza, M., Cerisola, G., Electrochim. Acta, 2005, 51, 191. [5] Pacheco, M.J., Morão, A., Lopes, A., Ciríaco L. , Gonçalves, I., Electrochim. Acta, 2007, 53, 629. [6] Ciríaco, L., Anjo, C., Correia, J., Pacheco, M. J., Lopes, A., Electrochim. Acta, 2009, 54, 1464. [7] Santos, V., Diogo, J., Pacheco, M.J.A., Ciríaco, L., Morão, A., Lopes, A., Chemosphere , 2010, 79, 637. September, 811, 2010. ISEL - Lisbon 22
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society K N 06 Assessing Performance and Degradation Mechanisms in Proton Exchange Membrane Fuel Cells C.M. Rangel, R.A. Silva, T.I. Paiva Laboratório Nacional de Energia e Geologia, Paço do Lumiar 22, Unidade de Pilhas de Combustível e Hidrogénio 1649-038 Lisboa, Portugal carmen.rangel@ineti.pt Fuel cells, considered the next generation of power sources, exhibit high generation efficiency and low environmental impact. From the different type of fuel cells available, the Proton Exchange Membrane Fuel Cell, PEMFC, has shown rapid development in the last decade, with a great increase in the power density to specific power ratio. Portable and mobile as well as stationary applications of fuel cells have been demonstrated. Furthermore, a variety of energy conversion applications, in association with renewable sources for fuel and oxidant supply, have been put forward and are seen as viable options in future highly distributed power generation. A considerable research effort in Materials Science and Electrochemistry is needed in order to increase the knowledge about fuel cells lifetime and reliability. In this work, the modular character of a PEM fuel cell will serve to examine the factors affecting performance, focussing on electrode kinetics and operating conditions together with the issues of thermal and water managements. A comparison will be done for PEM fuel cells fed by gas and liquid fuels emphasizing the effect on efficiency of the electrode kinetics, arising from multi-step fuel oxidation reactions and fuel crossover. The mechanism of ageing and degradation in fuel cells are not well understood. PEM fuel cell operates under very aggressive conditions in both anode and cathode. Increases in cell voltage leading to higher efficiencies may lead to surface oxidation of the supported catalyst, decreasing reaction activity and accelerating electrode degradation. In the case of fuel starvation, the anode potential may rise to levels compatible with the oxidization of water and if water is not available, oxidation of the carbon support will accelerate catalyst sintering. These issues will be addressed, in order to better categorize irreversible changes in the kinetic and/or transport properties of the cell, demonstrating the use of non-destructive electrochemical as well as ex-situ approaches. The contribution of mathematical modeling in PEM fuel cells will be also emphasized, focusing the prediction of conditions for a better thermal and water management and in aiding design and operating strategies. September, 811, 2010. ISEL - Lisbon 23
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