Modified Nafion 117 as an improved polymer electrolyte membrane for direct methanol fuel cells

Modification of the surface structure of the commercial ion exchange membrane Nafion(R)117, by low dose electron beam (EB) exposure, to produce an improved polymer electrolyte membrane for direct methanol fuel cells (DMFC) is described. Nafion 117 film was exposed to low dose EB irradiation, at an accelerating voltage of 35 kV. Subsequently the properties of the film itself, in terms of conductance, methanol permeability, percentage water uptake and shrinkage, together with the performance of its membrane electrode assembly in the DMFC were analyzed and contrasted with the untreated material. Low-dose EB treatment is shown to be effective in the reduction of methanol crossover, 600 muC/cm(2) exposure reducing crossover to 7% of that of the parent material. In terms of overall DMFC performance (maximum power output), improvements of up to 51% are reported in comparison to the use of untreated Nafion 117. A simple analytical protocol, allowing film properties to be directly related to subsequent DMFC performance, is also reported. IR reflectance (attenuated total reflectance) spectroscopy was used to study film surface composition and determine the effect of low-dose EB exposure on Nation 117 structure. These observations are contrasted with previous findings using traditional EB systems. (C) 2001 The Electrochemical Society.