Membrane Properties Control DMFC Performance and Efficiency: A Case of the Tail Wagging the Dog

The direct methanol fuel cell (DMFC) has significant but rather unfulfilled promise because of its poor performance and low efficiency despite using dilute feeds, in large part because of the use of Nafion^® membrane as the electrolyte. While this is well known, quantitative aspects of how the membrane transport characteristics affect the DMFC performance and efficiency are less well appreciated. We discuss a comprehensive analytical model that describes how the conductivity, water, methanol, and oxygen permeability of Nafion^® membrane affects the DMFC performance and efficiency. A comparison of experiments and theory is provided.

Thus, the model accurately predicts the effect of methanol crossover on open-circuit voltage (OCV) and on polarization of the fuel cell. It also correctly describes the effects of temperature and methanol feed concentration on DMFC performance. It describes the significant power losses because of electrode overpotentials and from methanol crossover, resulting in low DMFC efficiencies, except over a narrow range of conditions. The insightful model also allows theoretical design of membrane properties for improved performance.