| This investigation of the characteristics of direct methanol fuel cells (DMFC) has led to significant improvement in their performance. The methanol permeability of Nafion polymer electrolyte membranes has been measured in a DMFC by chronoamperometry. The activation energy for methanol diffusion was determined to be 25 kJ mol-1.;Methanol crossover reduces the performance of the DMFC. Several polypyrrole/Nafion composite membranes were prepared and have been shown to be significantly less permeable to methanol. DMFC performances achieved with some of these polypyrrole/Nafion composite membranes have outperformed those for, unmodified Nafion membranes. However, their performances have been shown to be strongly affected by the modification method. Membranes modified by Fe3+ oxidation of pyrrole have shown poor bonding with the electrodes, whereas use of H2O2 generally yields better results. The performance gains with the composite membranes are due to better cathode activity as a result of methanol crossover reduction. |
