Development of polypyrrole/Nafion composite membranes and a dynamic hydrogen reference electrode for direct methanol fuel cells.

摘要

One major goal of this research was to increase the fuel efficiency and cell performance of direct methanol fuel cells (DMFCs) by decreasing the methanol crossover from the anode to the cathode. Polypyrrole/Nafion composite membranes were prepared, and factors influencing the modification procedures were studied. An optimized, reproducible modification procedure was developed. The composite membranes outperformed pure Nafion 115 but need a longer activation time. The polarization and electrochemical impedance spectroscopy measurements showed that the activation process was due to two main factors: slow membrane hydration and slow cathode activation. The composite membranes showed an over 40% reduction in methanol crossover and a 70% increase in membrane resistance relative to Nafion 115. To further decrease the membrane resistance, counter ions were provided in the modification process. Poly[3-(pyrrole-1-yl)propanesulfonate]/Nafion composite membranes were also prepared to address this problem.;Another major goal was to develop and characterize a micro reference electrode to resolve the anode and cathode behavior in a fuel cell. An edge type Pt wire Dynamic Hydrogen Electrode (DHE) reference electrode was developed and used in a hydrogen proton exchange membrane fuel cell and a DMFC. The advantage of this DHE is that it is easy to use and does not require modification of the fuel cell hardware. This reference electrode provided good qualitative information. However, potential drift over long times makes it inappropriate for long-term measurements.