One-Dimensional Mathematical Model Of Direct Methanol Fuel Cell

Direct methanol fuel cell is recognized as a new alternative to the present power sources because of its high efficiency, high power density, low emission and easy fuel carriage. Liquid feed DMFC is receiving more attention because it is more convenient to use in practice. However, the wide application of DMFC is still hindered by two technological problems: low electro-activity of methanol oxidation on the anode and substantial methanol crossover through the polymer membrane from the anode to cathode.In order to better understand the processes and phenomena that determine the performance of a liquid feed DMFC, an isothermal, steady-state, one-dimensional mathematical model of DMFC is established. The spherical agglomerate model is used to describe the structure of catalyst layer in both electrodes. The kinetics of methanol oxidation is described by complicated mechanism. In particular, the model fully accounts for methanol oxidation and the effect of methanol oxidation on the oxygen reduction reaction in cathode catalyst layer. Also, in this model the transport phenomena and electrochemical kinetics of methanol in cathode catalyst layer and cathode diffusion layer are discussed. The velocity of the liquid mixture is determined by the liquid mass conservation equation and momentum conservation equation. The results of the numerical simulation include the distribution of the concentration of methanol, the mol fraction of oxygen, the proton current density and the overpotential losses. In addition, the influence of operational conditions, methanol crossover, structure parameters of DMFC, and electrochemical kinetic parameters on the performance of the DMFC is discussed in detail.The simulation results show that the concentration gradient of methanol in anode catalyst layer is greater than that in other layers. The concentration gradient of oxygen in cathode catalyst layer is greater than all the other layers. The concentration gradient of methanol in cathode catalyst layer is small. The results also show that increased temperature and pressure can enhance the performance of DMFC, and the concentration of methanol play an important role in DMFC performance. In addition, diffusion layer porosity and catalyst porosity play an important role in DMFC performance. At low current density, the effect of methanol crossover on the performance of DMFC is quite substantial. As current density increases, the effect of methanol crossover on the performance of DMFC becomes less significant.