Mathematical modeling of a direct methanol fuel cell

In order to maximize the performance of a complete DMFC, the anode and cathode were individually examined with modeling and experimental design testing. An isothermal, steady-state, mathematical model of a direct methanol fed, polymer electrolyte fuel cell (DMFC) has been developed. The model is of a membrane electrode assembly (MEA) supplied with aqueous methanol to the anode and gaseous oxygen to the cathode. The anode and cathode are considered to be porous electrodes consisting of an electronically conducting catalyst structure (matrix layer) that is thinly coated with an ion-selective polymer electrolyte (bond layer). A sensitivity analysis, performed on an agglomerate model of the anode, indicates that the most sensitive parameters to the prediction of DMFC anodic cell behavior are: the combination of exchange current density and specific surface area of the catalyst, the conductivity of the polymer electrolyte, and the thickness of the anode. Two cell performance limiting phenomena that occur in the cathode were investigated: the electrochemical oxidation of methanol that crosses over to the cathode, and oxygen transport limitations. The DMFC model quantitatively demonstrates that methanol electrochemically reacts in the cathode. The model also clearly shows that even at high current densities oxygen is present throughout the void volume of the cathode but the transport of oxygen through the bond layer to the catalyst particles limits the rate at which oxygen is electrochemically accessible.