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- New proton conductive membranes of indazole- and condensed pyrazolebisphosphonic acid-Nafion membranes for PEMFCPublication . Teixeira, Fatima; Teixeira, António P. S.; Rangel, C. M.ABSTRACT: The global demands of energy are still increasing alongside many civilizational problems, notably the effects on the environment due to the overuse of traditional energy sources based on fossil fuels. New cleaner, renewable sources for sustainable energy systems are a key challenge of the 21st century society.
- Novas membranas condutoras de protões para células de combustívelPublication . Teixeira, Fatima; Teixeira, António P. S.; Rangel, C. M.RESUMO: As membranas de permuta protónica continuam a ser um material fundamental e um desafio chave no desenvolvimento das células de combustível. Neste trabalho foram preparadas, usando um método de casting, novas membranas de Nafion dopadas com 1 wt% de diferentes ácidos bisfosfónicos (BPs). As novas membranas foram avaliadas relativamente à sua capacidade de absorção de água (water uptake), por gravimetria, à sua capacidade de troca iónica (IEC), através da determinação da presença de grupos ionizáveis na membrana utilizando titulação potenciométrica ácido-base, e ao grau de hidratação. As novas membranas apresentaram valores superiores aos da membrana de Nafion utilizada como referência. A condutividade protónica das novas membranas foi avaliada por Espectroscopia de Impedância Eletroquímica (EIS), em diferentes condições de humidade relativa e de temperatura, tendo apresentado valores de condutividade protónica superiores às da membrana comercial de Nafion em todas as temperaturas e humidades relativas testadas.
- 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.
- Síntese de fosfonatos e avaliação da sua atividade anti-inflamatória e antioxidantePublication . Lopes, Daniela; Parente, Helena; Martins, M. R.; Teixeira, Fatima; Teixeira, António P. S.
- 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).
- Chemical stability of new nafion membranes doped with bisphosphonic acids under Fenton oxidative conditionsPublication . Teixeira, Fatima; Teixeira, António P. S.; Rangel, C. M.ABSTRACT: The development of new proton exchange membranes for PEM technology in fuel cells and electrolysers with increased durability is paramount to system's lifetime and scalability. In this work, new modified Nafion membranes doped with bisphosphonic acids are proposed with increased resilience to chemical degradation by H2O2/Fe2+, mimicking ex-situ radical attack to membrane structure. Relevant properties were evaluated throughout Fenton's test using fluoride ion release and gravimetry determinations, and by ATR-FTIR spectros-copy and SEM before and after the chemical degradation. The new membranes showed a very good chemical stability after oxidative degradation under Fenton's test conditions at 80 degrees C, with more durability than Nafion 115 commercial membrane. After chemical degradation, the proton conduction of the membranes was assessed through EIS which reveals a decrease in the proton conductivity of all membranes, with the new modified membranes showing a smaller decrease of their proton conduction properties than Nafion 115 membrane. Fluoride ion release, weight loss measurements and ATR-FTIR spectros-copy data analysis suggest degradation of the side chain of the ionomer.
- New 1-Hydroxy-1,1-bisphosphonates derived from 1H-Pyrazolo[3,4-b]pyridine: Synthesis and CharacterizationPublication . Teixeira, Fatima; Lucas, Carla; Curto, Maria João Marcelo; Neves, M.; Duarte, M. Teresa; Andre, Vania; Teixeira, António P. S.A number of 1H-pyrazolo[3,4-b]pyridine derivatives, starting from 2-chloro-3-formyl pyridine, was synthesized to obtain new 1-hydroxybisphosphonates, a class of compounds with potential biological interest. Spectroscopic data were used to characterize all compounds and to identify N-1 and N-2 regioisomers, and mono- and bisphosphonates derivatives. X-ray diffractometry studies of compound 7a confirmed the proposed structure.
- New SPEEK doped membranes for ion exchange polymer electrolytes [Poster]Publication . Teixeira, Fatima; Teixeira, António P. S.; Rangel, C. M.
- 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.
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