Investigation of passive DMFC mini-stacks at ambient temperature

Two designs of flow fields/current collectors for a passive direct methanol fuel cell (DMFC) monopolar three-cell stack were investigated. The first one (A) consisted of two plastic plates covered by thin gold film current collectors in the area of electrodes with a distribution of holes through which methanol (from a reservoir) and air (from ambient) could diffuse into the electrodes. The second design (B) consisted of thin gold film deposited on the external borders of the fuel and oxidant apertures where the electrodes were placed in contact. A big central hole allowed a direct exposure of electrodes to ambient air (for the cathodes) and methanol solution (for the anodes). An investigation of the performance and discharge behaviour of the two designs was carried out. The advantages and disadvantages of each configuration were analysed. Similar performances in terms of maximum power were recorded; whereas, better mass transport characteristics were obtained with the design B. On the contrary, open circuit voltage (OCV) and stack voltage at low current were higher for the design A as a consequence of lower methanol cross-over. A longer discharge time (17 h) with a unique MeOH charge was recorded with design B at 250 mA compared to the design A (5 h). This was attributed to an easier CO2 removal from the anode and better mass transport properties.