Desenvolvimento de Membranas Condutoras de Prótons Baseadas em Poliuretanos e Líquidos Iônicos Próticos

Abstract

Fuel cells (FC) are devices that convert the chemical energy from an oxidation reaction into electrical energy. Among the different types of FC, the proton exchange membrane FC predominates. It has attractive traits like high power density, quick startup and high efficiency. However, problems originated from its operation at low temperatures have prevented its market expansion. Operation at high temperatures overcomes these problems, but it brings the necessity of humidification to certain membranes whose ionic conductivity depends on water. One of the possible solutions is the use of a polyurethane membrane, because of their potential versatility due to the vast possibility of combination between monomers, doped with protic ionic liquids, that possess a reactive proton, making it attractive for its use on fuel cells. Therefore, the goal of this study was to introduce different ionic liquids in a poly(urethane urea) membrane, varying the size of the apolar chain of the ionic liquid and its content. The membranes were characterized in terms of ionic conductivity, thermal resistance and morphology. The ionic conductivity found was at least two orders of magnitude lower than those of the commercial membrane used in this application. The introduction of the ionic liquid lowered the thermal resistance of the material, but raised the resistance to ethanol, one of the potential fuels for FC. Beyond that, different characterization techniques indicated interaction between the ionic liquids and the flexible domains of polymer chains, with larger apolar chains showing stronger interactions.