PTFE coated Nafion proton conducting membranes for direct methanol fuel cells

The performances of direct methanol fuel cells (DMFC) are affected by the methanol cross-over, due to the concentration gradient and electrosmosis between the anodes and cathodes. In this study, Polytetrafluorethylene (PTFE) has been sputter deposited on conventional proton conducting membranes, Nafion117. It was found that the problem of the methanol cross-over was eased by the PTFE coating. The properties of coated and uncoated Nafion117 were investigated by scanning electron microscopy, electron spectroscopy for chemical analysis, gas chromatography and AC impedance spectroscopy. The coated film can form a barrier layer between the methanol solution and the polymer membrane. The PTFE barrier layer can effectively retard the methanol molecules, whereas the proton conductivities were not significantly influenced. The conductivity/permeability ratio two times higher the conventional Nafion117 membrane has been achieved under an optimized coating time. This technique developed shows great potential for the applications in DMFCs. (C) 2010 Elsevier B.V. All rights reserved.