Modification of the surface structure of the commercial ion exchange membrane Nafion®117, by low dose electron beam ͑EB͒ exposure, to produce an improved polymer electrolyte membrane for direct methanol fuel cells ͑DMFC͒ 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 C/cm 2 exposure reducing crossover to 7% of that of the parent material. In terms of overall DMFC performance ͑maximum power output͒, 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 reflectance͒ spectroscopy was used to study film surface composition and determine the effect of low-dose EB exposure on Nafion 117 structure. These observations are contrasted with previous findings using traditional EB systems.International interest in both renewable power sources and alternatives to curb current fuel emission levels makes the development of a new fuel cell system an attractive proposition. On consideration of the main issues, such as safety, device fabrication, market, costs, and potential applications, the direct methanol fuel cell ͑DMFC͒ appears to be the system of choice. This view is supported by the vast number of research groups, including academic, industrial, and governmental laboratories, currently targeting the development of DMFCs for a wide range of potential uses, from portable power sources for small electronic devices to vehicular applications. Although major steps forward have been achieved in terms of DMFC design since the onset of research in this area, further developments allowing widespread commercialization of this technology are more likely to come from improvements in the central DMFC components.Although a number of other factors directly influence performance, the operational part of the DMFC can be thought of in terms of having two main features, the electrodes and the polymerelectrolyte membrane. Looking at the basic DMFC design and mode of operation, improving catalytic activity at the cathode and reducing the extent of methanol crossover through the polymer-electrolyte membrane can be identified as two ways of improving overall cell performance. During operation methanol is fed into the system at the anode, where it is oxidized generating carbon dioxide ͓CH 3 OH ϩ H 2 O → CO 2 ϩ 6H ϩ ϩ 6e Ϫ ͔, while the corresponding reduction process takes place at the cathode ͓4H ϩ ϩ O 2 ϩ 4e Ϫ → 2H 2 O͔. However, due to the similar composition of the two electrodes, if methanol crossover through the polymer-electrolyte membran...
