(277e) Modeling of Methanol Crossover Across Polymer Electrolyte Membranes and Its Effect On the Performance of Passive DMFCs

Passive Direct Methanol Fuel Cells (PDMFCs) are a potentially attractive power source for portable applications, due to their high power density, easy fuel storage, and the ability to run at completely ambient conditions. However, design and development of a truly passive, air-breathing, orientation-independent, compact PDMFC fueled by neat methanol that can compete effectively with ever-improving batteries for low wattage portable power for consumer or military applications has proved to be challenging. Improved theoretical understanding of the fundamental transport and reaction processes within PDMFCs can help, which is the goal of this work. A relatively simple model is described resulting in analytical solutions that can provide important insights into the factors that limit PDMFC performance. The key factor limiting performance is the facile methanol crossover across the polymer electrolyte membrane (PEM), resulting in poor performance, energy density, and efficiency. In other words, the PEM does not perform well at one of its essential functions, that of keeping the fuel and the oxygen apart. As a result, the key challenge in PDMFCs is how to passively balance the neat methanol flux to maintain a low concentration at the anode at any current density. Our analytical model clearly explains the effects of methanol crossover via diffusion and electro-osmosis through the PEM on the overall performance and efficiency of PDMFC under various operating conditions.