Effects of Operating Conditions on Direct Methanol Fuel Cell Performance Using Nafion-Based Polymer Electrolytes

Systematic experiments were carried out to study the effects of various operating conditions on the performances of a direct methanol fuel cell (DMFC) using Nafion 117 and its modified membranes. The cell performance was studied as a function of cell operating temperature, methanol concentration, methanol flow rate, oxygen flow rate, and methanol-to-oxygen stoichiometric ratio. The experimental results revealed that the most significant factor was the temperature, increasing the cell performance from 50 to 80 degrees C. We achieved the maximum power density (P-max) of 86.4 mW cm(-2) for a DMFC at 80 degrees C fed with 1 M methanol (flow rate of 2 ml min(-1)) and humidified oxygen (80 ml min(-1)). A methanol concentration of 1 M gave much better performance than using 3 M of methanol solution. The oxygen and methanol flow rates with the same stoichiometric ratio had a beneficial effect on cell performance up to certain values, beyond which further increase in flow rate had limited effect. The V-oc using argon plasma-modified Nafion was higher than the pristine Nafion membrane for the cell operated on 3 M methanol solution, which was due to the lower methanol permeability of the Ar-modified Nafion.