Water and methanol crossover in direct methanol fuel cells - Effect of anode diffusion media

Various anode diffusion media have been experimentally studied to reduce water crossover in a direct methanol fuel cell (DMFC). A two-phase water transport model was also employed to theoretically study their effects on water transport and saturation level in a DMFC anode. It is found that wettability of the anode microporous layer (MPL) has a dramatic effect on water crossover or the water transport coefficient (alpha) through the membrane. Under different current densities, the MEA with a hydrophobic anode MPL has consistently low alpha, several times smaller than those with a hydrophilic MPL or without an anode MPL. Methanol transport in the anode is found to be not influenced by a hydrophobic anode MPL but inhibited by a hydrophilic one. Constant-current discharge shows that the MEA with hydrophobic anode MPL displays much smaller voltage fluctuation than that with the hydrophilic one. A modeling study of anode water transport reveals that the liquid saturation in the anode is lowered significantly with the increase of anode MPL contact angle, which is thus identified as a key parameter to minimize water crossover in a DMFC. (C) 2008 Elsevier Ltd. All rights reserved.