Development of a passive direct methanol fuel cell stack for high methanol concentration

In order to develop a vertically arranged passive DMFC with a porous carbon plate, PCP, the effect of the head height of the methanol solution in contact with the porous carbon plate on the power generation was investigated for a 55 mm height using a single cell. The single cell was operated at several methanol concentrations greater than 70 wt%. By filling the reservoir with 90 and 100 wt% methanol solutions, power densities greater than 30 mW cm⁻² for over 10 h were demonstrated. Based on the result of the single cell study, a passive DMFC stack consisting of 8 unit cells with the PCP was designed and fabricated. The power generation characteristics were then experimentally measured. The maximum power output of 1.8 W, which was almost 10% lower than that expected from the single cell performance, was obtained with 100% methanol. At the same time, a nonuniform cell voltage among the 8 unit cells was found as a reason for the decreasing power output with the increasing current.