Membranas condutoras de prótons a base de alginato de sódio e líquidos iônicos próticos

Abstract

Fuel cells (FC) are devices that convert the chemical energy of a fuel oxidation reaction into electrical energy. Among the different types of FC, those based on proton exchange membranes (PEM) are the most flexible, exhibiting characteristics such as high energy density, quick start, and high efficiency. This type of fuel cell is ideal for transport, portable and stationary energy applications. However, its use at low temperatures creates limitations, which can be overcome by operation at temperatures above 100 °C. Moreover, some of the most commercially used membranes depend on the presence of water in their structure for proton transport. One of the possible solutions is the addition, to the membrane, of materials that do not depend on the presence of water for the proton conductivity, such as protic ionic liquids (PIL). The PIL have a reactive proton, making them attractive to be used in proton exchange membranes (PEM). The addition of these PIL to an ionic polymer matrix, such as sodium alginate (NaAlg), presents an alternative to the PEM currently used. Thus, the main goal of this thesis was to introduce different PIL to a polymeric matrix of NaAlg and to verify the ability of the produced membrane in the conduction of protons at more elevate temperatures. Initially, a study was carried out with different PIL to select those that would be added to the NaAlg matrix to produce the membranes. Then, these membranes were characterized concerning their morphology, thermal resistance, mechanical resistance, and conductivity. It was concluded that the drying method and the compatibility between the PIL and the polymeric matrix significantly influenced the morphology and properties of the membrane. A greater compatibility between the PIL and the polymer and a better distribution of the PIL throughout the polymeric matrix led to higher conductivity values, although materials presenting lower thermal and mechanical resistance have been produced, as consequence. Membranes with electrochemical, thermal and mechanical properties in the same order of magnitude as promising membranes found in the literature for the proposed application were obtained.