http://hdl.handle.net/10174/142 2026-04-03T19:46:56Z 2026-04-03T19:46:56Z Teixeira, António P. S. Teixeira, Fátima C. Sá, Ana I. de Rangel, C. M. http://hdl.handle.net/10174/26474 2020-01-20T14:53:59Z 2019-08-31T23:00:00Z

Title: New Proton Conductive Heteroaromatic Bisphosphonic acid-Nafion Membranes for PEMFC Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Sá, Ana I. de; 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 storable 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). These membranes strongly depend on the presence of conducting water or other electrolyte content, which limits their operation to 80 ºC. In order to advance novel membranes for application in PEMFCs, we have developed a series of bisphosphonic acid derivatives, which are used as dopants. Herein, we present the preparation and characterization of the new Nafion doped membranes, and the evaluation of their proton conductivity at different temperature and relative humidity (RH) conditions. In this work, new Nafion doped membranes were prepared and their proton conductivity were evaluated. The incorporation of BPs dopants on Nafion polymer enhances the proton conductivities of the new membranes, with all membranes showing higher proton conductivities than Nafion.

2019-08-31T23:00:00Z Teixeira, António P. S. Teixeira, Fátima C. Sá, Ana I. de Rangel, C. M. Ortiz-Martínez, V. M. Ortiz, A. Ortiz, I. http://hdl.handle.net/10174/26472 2020-01-20T14:49:54Z 2019-05-31T23:00:00Z

Title: New modified Nafion-biphosphonic acid composite membranes for enhanced proton conductivity and PEMFC performance Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Sá, Ana I. de; Rangel, C. M.; Ortiz-Martínez, V. M.; Ortiz, A.; Ortiz, I. 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.

2019-05-31T23:00:00Z Teixeira, António P. S. Teixeira, Fátima C. Rangel, Carmen M. Sá, Ana I. de http://hdl.handle.net/10174/24379 2019-01-31T11:08:05Z 2018-08-31T23:00:00Z

Title: Proton conductivity of Nafion-azolebisphosphonates membranes for PEM fuel cells Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Rangel, Carmen M.; Sá, Ana I. de 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 [1]. 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.

2018-08-31T23:00:00Z Teixeira, António P. S. Teixeira, Fátima C. Rangel, Carmen M. Sá, Ana I. de http://hdl.handle.net/10174/24378 2019-01-31T11:07:35Z 2018-06-30T23:00:00Z

Title: Nafion® phosphonic acid composite membranes for proton exchange membranes fuel cells Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Rangel, Carmen M.; Sá, Ana I. de Abstract: The fuel cells are electrochemical devices that convert the chemical energy stored in a fuel, directly and efficiently into electrical energy. Among the fuel cells, the proton exchange membrane fuel cells (PEMFCs) are considered promising power sources, due to their high power density and high power-to-weight ratio and the proton exchange membranes are considered a key material for the operation of these cells. Usually, these membranes are made of organic polymers containing acidic functionalities, but their proton transport properties strongly depend on their water content, which limit their operation temperatures up to 90ºC. These limitations have fostered the interest in research and development of new alternative membranes [1,2]. In order to develop novel membranes for application in PEMFCs, we have synthesized and characterized mono- or 1,4-dissubstituted aryl derivatives with phosphonic (PAs) and bisphosphonic acids (BPs) groups (Fig. 1). The new Nafion® membranes, doped with PAs or BPs, were prepared and characterized. Their proton conductivity was evaluated by electrochemical impedance spectroscopy (EIS) to analyse the influence of the structure of dopants and the method of the preparation of the membranes.

2018-06-30T23:00:00Z