The water transport characteristics of the passive DFAFC were investigated to obtain a general understanding of the water transport characteristics through the membrane in the DFAFC in this study. Effects of the current density, membrane thickness and formic acid concentration on the water flux thorough the membrane in the passive DFAFC were investigated and they were compared with those of the DMFC and the PEFC. It was found that the water crossover through the membrane of the passive DFAFC linearly increased with increasing current density irrespective of the membrane thickness similar to the DMFC; however, the water flux was smaller than that of the DMFC. Referring to the effect of the membrane thickness on the water flux, the water flux from the anode to the cathode increased with increasing the membrane thickness in the DFAFC, although it decreased with increasing membrane thickness in the DMFC. Moreover, the water flux increased with decreasing fuel concentration in the DFAFC, although the water crossover in the DMFC was not influenced by the fuel concentration. From these results, it was found that the water transport characteristics in the DFAFC were different from those in the DMFC. (C) 2013 Elsevier B.V. All rights reserved.