Separate measurement of current density under land and channel in Direct Methanol Fuel Cells

•Current densities under the land and channel are separately measured in DMFCs.•Current density is much higher under the land than that under the channel.•The main reason for the higher current density is the much higher ECA under the land.

The knowledge of where current density is higher, under the land or channel in a direct methanol fuel cell (DMFC) and the mechanisms are very important for flow-field design optimizations. Such information could also lead to solutions to mitigate methanol crossover and/or its effects. Therefore, a novel technique is used to directly measure the current density under the land and under the channel separately. In this method, the anode side of the cell is partially catalyzed depending on the area of interest, whereas the cathode side is always fully catalyzed. Experimental results show that, under all the operating conditions used, the current density under the land is always significantly higher than that under the channel. Under most operating conditions, the current density under the land is more than 100% higher than that under the channel, and sometimes, as high as three times higher in typical DMFC operating voltage ranges. Further study shows that one of the main causes for such a drastic difference is the much higher electrochemical active area (ECA) under the land. Additional experimental results also show the performance trends for the land or the channel at different methanol concentrations and different cathode reactants (air or oxygen).