An experimental and modeling based investigation into the high stoichiometric flow rates required in direct methanol fuel cells

Direct methanol fuel cells (DMFCs) characteristically require high stoichiometric flow rates in order to optimize their performance. Experiments and modeling were performed in order to provide an improved understanding of the physical basis of this requirement. Anode side modeling suggests that high stoichiometry is necessary to keep the carbon dioxide (CO2) gaseous volumetric generation rate to a fraction of the overall anode flow rate such that CO2 gaseous clogging may not result. This requires anode stoichiometries generally greater than 20, and higher with increasing molarity. Cathode side modeling and measurements show that saturated exit air is directly related to poor cell performance. The modeling suggests that the cathode side mass transfer effect is quite strong despite the laminar flow conditions. Stoichiometries greater than 5 are seen to reduce the cell's exit relative humidity (RH) and improve cell performance.