Influence of cathode oxygen transport on the discharging time of passive DMFC

In this paper, the long-term discharge performances of passive DMFC at different currents with different cell orientations were investigated. Water produced in the cathode was observed from the photographs taken by a digital camera. The results revealed that the passive DMFC with anode facing upward showed the best long-term discharge performance at high current. A few independent water droplets accumulated in cathode when the anode faced upward. Instead, in the passive DMFC with vertical orientation, a large amount of produced water flowed down along the surface of current collector. The passive DMFC with vertical orientation showed relatively good performance at low current. It was concluded that the cathode produced less water in a certain period of time at smaller current. In addition, the rate of methanol crossover in the passive DMFC with anode facing upward was relatively high, which leaded to a more rapid decrease of the methanol concentration in anode. The passive DMFC with anode facing downward resulted in the worst performance because it was very difficult to remove CO2 bubbles produced in the anode.