Water vapour absorption in new liquid crystalline membranes with sulfonic groups for DMFC

Abstract

Direct Methanol and Ethanol Fuel Cells (DMFC and DEFC, respectively) are interesting alternatives for conventional energy conversion systems, allowing for the use of bio-fuels and other renewable energy sources. Despite their high efficiencies and low environmental impact, they still present some limitations to be overcome prior to their use at a commercial scale. Such is the case of alcohol crossover through the electrolyte, from the anode to the cathode, which causes serious efficiency drops in the cells. Attempts to reduce crossover usually involve a rational design of the polymeric electrolytes membranes (PEM) used in DMFC and DEFC. Under this view, a new set of liquid crystalline materials are under development and investigation to obtain a better morphology control and optimised transport properties of solvents (water, methanol, ethanol) in the membranes.

In this framework, this Master Thesis (MT) studies the absorption of vapour in acrylic membranes containing liquid crystal polymers for their future use as future externally controlled electrolytes in fuel cells fed by bio-alcohols. The side-chain copolymers contain azobenzenic units (liquid crystalline), terminal sulfonic groups (to enhance proton conductivity) and methacrylate (to enhance the flexibility of the membranes).

A pressure decay equipment was set-up and utilised at different temperatures. The experiments were controlled by LabView, and some modifications were performed to the program in order to improve the data acquisition. Despite the low water absorption observed in the materials, the results show an increase in the solubility of the membranes with higher sulfonic and lower azobenzenic contents. This fact suggests the possibility to improve the water absorption through a combination of chemical composition/LC phase formation.