http://hdl.handle.net/10174/29587 Sun, 05 Apr 2026 13:27:56 GMT 2026-04-05T13:27:56Z http://hdl.handle.net/10174/40786 Title: New membranes for CO2 electrochemical reduction Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Rangel, C. M.; Messias, S.; Martins, R.; Mendes, J. M.; Reis Machado, Ana S. Abstract: The use of CO2 as a valuable feedstock to obtain new useful fuels and materials, such as CO, alcohols, formic acid and hydrocarbons, has become an important research field that can contribute to valuable strategies in carbon resource utilization, such as the Electrochemical CO2 Reduction (ECR). The process is carried out in electrolyzers, which have a membrane as a key component to separate the two-half cells, with performance and sustainability strongly linked to membrane properties, including ionic conductivity, chemical and structural stability and permeability of products and incoming and generated gases [1]. The aim of this work is the preparation and evaluation of a series of doped cation conductive membranes for use in low temperature CO2 electrolysis, for increasing efficiency and minimizing gas crossover. The new membranes were prepared by the incorporation of bisphosphonic acids dopants into the matrix of selected polymers: widely used Nafion, and a lower cost, non-fluorinated alternative, SPEEK. The choice of dopants is justified since their incorporation improved ion conducting properties of the membranes as well as their durability, as indicated in previous studies by the authors [2,3]. New membranes, with a 7x7 cm dimension, were tested in an optimized, two compartment, purposely build reactor for CO2 reduction [4], employed to obtain syngas, operating at 45 °C, pressurized at 10 bar, using 10% EMIMOTf ionic liquid as electrolyte and 1437 C of charge. Membrane performance was compared with a PSFA-based Nafion-like commercial membrane, 10120-PK from Fumatech, used as standard and tested in the same experimental conditions. Electrolyses results using the new membranes are compared in terms of productivities of CO2 reduced products, faradaic efficiencies, energy efficiencies and crossovers. These results showed that these membranes are a promising material for ECR. Sat, 31 May 2025 23:00:00 GMT http://hdl.handle.net/10174/40786 2025-05-31T23:00:00Z http://hdl.handle.net/10174/40696 Title: Enhancing Conductivity in PEM Chitosan Membranes through Bisphosphonate Graphene Oxide Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Rangel, C. M.; Naffati, Naima Abstract: Proton exchange membranes (PEM) are a key component on several electrochemical devices, such as fuel cells and electrolysers, and hold great promises for various technological applications. However, their properties, including their limited proton conductivity, remain a significant challenge. In this study, a novel approach to improve the conductivity of chitosan membranes was used, through the incorporation of bisphosphonate graphene oxides (BPGO) as dopants. Starting from two graphene oxide materials with different oxidation levels, new BPGOs were achieved using a one-pot synthetic procedure. These dopants were characterized by ATR-FTIR and XPS spectroscopies. To improve the proton transport properties of membranes, new BPGO dopants were incorporated into the chitosan matrix, using a casting method, to achieve new chitosan doped membranes. These membranes were systematically studied to assess their proton conduction properties by impedance spectroscopy. The results demonstrate their the incorporation of these BPGOs dopants increases the proton conductivity of the membranes, with a significant increase in proton conductivity upon doping with high oxidation level BPGO, with a maximum enhancement of 1% (só ???) observed at an optimal doping level. The unique structure of BPGO, with its abundant functional groups and high specific surface area, facilitates the proton conduction of the membrane. Additionally, the presence of bisphosphonate groups improves the proton conductivity of the membrane, which increases with the increment of this functional group presents in the dopant. Fri, 31 May 2024 23:00:00 GMT http://hdl.handle.net/10174/40696 2024-05-31T23:00:00Z http://hdl.handle.net/10174/40664 Title: Chitosan doped membranes for electrochemical devices Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Rangel, C. M.; Naffati, Naima Abstract: The development of new proton exchange membrane (PEM) for electrochemical devices, such as fuel cells and electrolyzers, have attracted researcher’s attention in the pursuit for more sustainable and cost-effective technologies for clean energy production, being extensive those for CO2 reduction and conversion1,2. To this end, in the present work, new modified chitosan (CS) membranes doped with ionic liquids (ILs) were developed to perform as PEM at those electrochemical devices, as an alternative to widely used commercial Nafion, with several advantages such as wider availability, lower cost, biodegradability and thermal stability. These modified membranes for use in electrochemical devices are expected to show suitably enhanced ion conductivity and also improved mechanical strength associated to a decrease in water uptake. Sun, 30 Jun 2024 23:00:00 GMT http://hdl.handle.net/10174/40664 2024-06-30T23:00:00Z http://hdl.handle.net/10174/40627 Title: New SPEEK Membranes Modified with Bisphosphonate Dopants Authors: Teixeira, António P. S.; Teixeira, Fátima C.; Rangel, C. M. Abstract: Sustainable emerging energy technologies are pivotal to a decarbonized society that still continuously increases its energy demands. Fuel cells and eletrolyzers are part of these promising sustainable technologies, but they still depend on several factors, especially on their membranes. These are a key component acting as a separator, between their different materials and electrolytes of different devices’ compartments, and as a selective ion-exchange barrier, controlling the ion flow and species permeability. Sulfonated poly(etheretherketone) (SPEEK) polymer is a versatile non-fluorinated alternative, as a low-cost and more environmentally friendly membrane, to the most commercially successful membrane based on the perfluorinated sulfonic Nafion®. Also, our previous studies showed that the incorporation of BPs dopants into the polymeric matrices, modifies the properties of the doped membranes, including their proton conduction and durability.1-5 Following these results, a set of diverse bisphosphonates were prepared from different synthetic strategies and characterized by NMR, IR and mass spectrometry. The SPEEK polymer was prepared by a sulfonation reaction from poly(etheretherketone) (PEEK), to afford a polymer with a sulfonation degree of 57%. The new dopants were incorporated by a casting method into SPEEK matrices to obtain the new modified membranes. The doped membranes were analyzed by NMR and ATR-FTIR spectroscopy and their proton conductivity was assessed by electrochemical impedance spectroscopy (EIS) at different temperatures, ranging from 30 to 60 ºC, under 100% RH conditions. Sun, 31 Aug 2025 23:00:00 GMT http://hdl.handle.net/10174/40627 2025-08-31T23:00:00Z