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- Gold deposition from 1-butyl-1-methyl-pyrrolidinium dicyanamide ionic liquid at open-circuit and under potentiostatic controlPublication . Sá, A.I. De; Eugénio, S.; Quaresma, S.; Rangel, C. M.; Vilar, R.In this work, the deposition of gold on copper substrates from solutions of HAuCl4.3H2O in 1-butyl-1-methylpyrrolidinium dicyanamide was studied. Deposition was carried out in open-circuit and under potentiostatic control at temperatures from 293 to 353 K, in normal atmosphere, with deposition conditions allowing water from atmospheric absorption up to 0.8 wt.%. Films of gold were obtained by both methods. Deposition at open-circuit occurs by galvanic displacement mechanism. Involvement of Cu+ species in the electrodeposition process was suggested by cyclic voltammetry. Furthermore, copper incorporation in the gold films was confirmed by X-ray diffraction. SEM observation and XRD analysis show that films are nanocrystalline with a globular morphology except for the films formed under potentiostatic control at 353 K, which show a dendritic structure. The size of the crystallites determined by Scherrer's equation varies in the range from 6 to 25 nm.
- Enhanced proton conductivity of Nafion-azolebisphosphonate membranes for PEM fuel cellsPublication . Teixeira, Fatima; de Sá, A.I.; Teixeira, António P. S.; Rangel, C. M.ABSTRACT: Fuel cells are among the cleaner alternatives of sustainable energy technologies, where their proton exchange membranes continue to be a key component with many challenges and opportunities ahead. In this study, different indazole- and benzotriazolebisphosphonic acids were prepared and incorporated into new Nafion-doped membranes up to a 5 wt% loading. The new membranes were characterised, and their proton conductivities were evaluated using electrochemical impedance spectroscopy. Membranes with a 1 wt% loading showed better proton conductivities than Nafion N-115 at all temperature and under relative humidity conditions studied. In these conditions, the best value was observed for the membrane doped with [hydroxy(1H-indazol-3-yl)methanediyl]bis(phosphonic acid) (BP2), with a proton conductivity of 98 mS cm(-1). Activation energy (E-a) values suggests that both Grotthuss and vehicular mechanisms are involved in the proton conduction across the membrane.
- Environmental impact assessment of the penetration of hydrogen technologies in Portugal's road transportPublication . Travassos, Maria Antónia; Sá, A.I. De; Luz, Paulo P. da; Rangel, C. M.Road traffic is one of the transportation sectors with faster growth and also one of the most important emitters of greenhouse gases (GHGs). In this work, an analysis of the environmental benefits resulting from the introduction of hydrogen on road transport in Portugal is made. Impact is analyzed mainly looking at the pollutant emissions provided by road transport at the point of use. Emissions associated to road transport have been estimated using the software COPERT (version 4), since it provides a detailed methodology for each specific pollutant related to the vehicle fleet of a region or country, as well as the driving conditions and fuel consumption. Passenger cars, light duty vehicles and public transport buses are the vehicles categories in which the hydrogen technology is foreseen. The hydrogen penetration rates (moderate and high) are extracted from the European Project HYWAYS. Two trends are then considered, which give penetration rates of 40.0 % and 74.5 % in 2050 for the moderate and high scenarios respectively.
- Enhancing Pt electrocatalytic activity by surface functionalization of carbon support with aromatic sulphonic groupsPublication . Capelo, Anabela; Esteves, M. Alexandra; de Sá, A.I.; Rangel, C. M.Preliminary results are presented for Pt deposited on 4-aminobenzenesulphonic acid-functionalized carbon, Pt/C_ABSA. Vulcan XC-72R was functionalized with the objective of influencing the dispersion of catalyst nanoparticles and to decrease the resistance of three phase boundaries, by introducing sulphonic groups. Electrochemical characterization of the supported catalyst was done in a 0.5 M sulphuric acid solution with added chloride and also using methanol demonstrating well defined features and stable voltammograms after 30 cycles, with apparent higher currents when compared with commercial catalyst. The structure sensitive adsorption of anions on platinum is confirmed by the blocking effect of chloride ions in the hydrogen adsorption-desorption region as well as by the consequent dissolution of platinum, evident in both anodic and cathodic features of the voltammograms regarding surface oxide formation and reduction. The partial reversibility of the effect of chloride ions is discussed. Research is in progress in order to accomplish a comprenhensive characterization of the synthesized catalyst and to ascertain the effect of the sulphonic groups.
- Proton conductivity of Nafion-azolebisphosphonates membranes for PEM fuel cellsPublication . Teixeira, Fatima; Sá, A.I. De; Teixeira, António P. S.; Rangel, C. M.ABSTRACT: Energy systems with cleaner and sustainable sources are crucial challenges of the 21st century to deal with the environmental threat of global warming and the declining reserves of fossil fuels. Fuel cells are electrochemical devices that convert the chemical energy stored in a fuel directly into electrical energy, providing electrical energy with high efficiency and low environmental impact. Among them, proton exchange membrane fuel cells (PEMFCs) are considered promising power sources, due to their high power density and high power-to-weight ratio but their performance depends crucially on their proton exchange membranes. Usually, these membranes are made of organic polymers containing acidic functionalities (ex. Nafion®), which proton transport properties strongly depend on their water content and, consequently, limit their operation temperatures up to 90ºC. Preliminary studies have demonstrated that incorporation of aryl-bisphosphonic acids into Nafion, by casting, results in an enhancement of the proton conductivity of the membrane. The aim of this work was the preparation of new Nafion membranes doped with azolebisphosphonates derivatives, which could act as a source of protons and also function as proton acceptors, facilitating the intermolecular transmission of protons through the membrane.
- New proton conductive heteroaromatic bisphosphonic acid-Nafion membranes for PEMFC [Resumo]Publication . Teixeira, Fatima; Sá, A.I. De; Teixeira, António P. S.; Rangel, C. M.ABSTRACT: The integration of new cleaner, renewable and environment-friendly sources and energy vectors for sustainable energy systems are a key challenge for 21st century society. Fuel cells are among the clean energy conversion technologies with vast applications and scope, introducing hydrogen as a flexible and storage energy vector and presenting a viable alternative to fossil fuels. Proton exchange membrane fuel cells (PEMFCs) are considered promising power sources, but their performance depends crucially on the properties of their proton exchange membranes (PEM).
- New modified Nafion-biphosphonic acid composite membranes for enhanced proton conductivity and PEMFC performance [Resumo]Publication . Teixeira, Fatima; Sá, A.I. De; Teixeira, António P. S.; Ortiz-Martínez, V. M.; Ortiz, A.; Ortiz, Inmaculada; Rangel, C. M.ABSTRACT: The performance of PEM fuel cells critically depends on their proton exchange membrane structural and chemical stabilities as well as on their proton conductivity. Limitations of commercially available Nafion membranes to operating at temperatures above 80 ºC have fostered the interest in research and development of new membranes [1,2]. The aim of this work is the preparation of new modified Nafion composite membranes, with a bisphosphonic acid moiety, a promising proton carrier exhibiting good proton donating/accepting properties and thermal stability. Synthesis and characterization were undertaken of a series of bisphosphonic acid derivatives and their incorporation into a Nafion matrix, by casting. The new membranes were characterized by ATR-FTIR and SEM along with their ion exchange capacity and water-uptake. The evaluation of their proton conductivity was carried out by electrochemical impedance spectroscopy, at various temperature and relative humidity (RH) conditions. The incorporation of BPs dopants enhances the proton conductivity, with all membranes exhibiting higher values than Nafion N-115, tested in the same experimental conditions. Selected membranes were integrated into a fuel cell MEA, using a single cell assembly, with an active area of 2.5x2.5 cm2 and a catalyst loading of 0.5 mgPtcm-2. Performance was evaluated, using an air fed cathode, at temperatures from 30 ºC to 80 ºC. Membrane doped with BP2 showed the best performance, with higher power density outputs than Nafion N-115 shown at all temperatures.
- Electronic properties of Al-Nb mixed oxide as a function of their compositionPublication . Di Quarto, F.; Santamaria, M.; Gentile, M. L.; de Sá, A.I.; Skeldon, P.; Thompson, G. E.; Rangel, C. M.
- Gold electrodeposition from ionic liquids: an alternative to conventional aqueous bathsPublication . Sá, A.I. De; Rangel, C. M.; Quaresma, S.; Eugénio, S.; Vilar, R.
- 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.
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