Water Management in a Passive DMFC Using Highly Concentrated Methanol Solution

A two-dimensional, steady state, nonisothermal, nonequilibrium, multifluid, two-phase flow model is employed to investigate fuel delivery characteristics, as well as the strong relation between water transport through the membrane and methanol crossover. A porous layer, called the fuel delivery layer, is used between the anode backing layer and the methanol reservoir to be able to employ high concentration methanol solution at the anode reservoir. A simple analytical model for liquid methanol distribution in the anode is presented to show the significant effect of water crossover through the membrane on the methanol dilution at the anode catalyst layer. A comprehensive numerical model is employed to verify the concept developed by the analytical model. The numerical model also accounts for the dissolved water phase in the Nafion membrane. Using a hydrophobic microporous layer at the cathode decreases methanol crossover due to a reduction in water crossover, as well as attaining a water neutral condition. It is found that thickening of the porous fuel delivery layer cannot alleviate the methanol crossover through the membrane without controlling the water transport. The results also show that a cathode microporous layer can significantly reduce the liquid saturation at the cathode backing layer which, in turn, reduces water flooding at the cathode.