Supported Nafion Membrane for Direct Methanol Fuel Cell

Abstract

The performances of direct methanol fuel cells are largely dependent on the methanol crossover, while the amount of methanol crossover is reported to strongly rely on membrane materials and thickness. In this research, two new membranes (Nafion 211 and Nx-424), along with well-known Nafion 117 and 112 were studied as electrolytes in the direct methanol fuel cells (DMFC). The Nafion 211 is the thinnest and latest membrane of Nafion series products and Nx-424 is a Nafion membrane with polytetrafluoroethylene (PTFE) fibers as mechanical reinforcement. Nx-424 is used primarily for chloro-alkali production and the electrolytic processes. Although open circuit voltage provides a quick way to evaluate the effect of methanol crossover, the amount of methanol crossover through the membranes was studied in detail via the electrochemical oxidation technique. Both methods show the same trend of methanol crossover of different membranes in this study. Nafion 211 was found to present the highest degree of methanol crossover, however, its’ best performance implied the fact that the influence of the cell resistance (membrane thickness) is dominated in the traditional Nafion system. Although Nafion membrane with thicker thickness and PTFE fiber within Nx-424 provided higher resistance for methanol to cross through, the negative effects of its’ hydrophobic properties also prevent the transport of H2O accompanied by the proton. Therefore, the cell performance of Nx-424 is lower both due to poor proton conductivity and thickest membrane. In other words, the cell performances of traditional Nafion series membranes (Nafion 211, 112, 117) were fully controlled by the thickness while Nx-424 was controlled both by its’ blend properties (hydrophilic-Nafion and hydrophobic-PTFE ) and thickness.