In-Situ Estimation of Faradaic Efficiency for a Direct Methanol Fuel Cell Stack by a Carbon Dioxide Saturated Solution Method

A direct methanol fuel cell (DMFC) system consisting of 40 single cells was assembled to study the influence of the transport phenomena at the anode and stack faradaic efficiencies by a CO₂ saturated solution method. This method corrected the common experimental error in measuring methanol crossover caused by the simultaneous CO₂ permeation from the anode to cathode. Both anode and stack faradaic efficiencies were estimated using this method. An equivalent “carbon-flow current” has been defined and a relationship between the transport phenomena and efficiencies was developed. Also the effect of methanol concentration, methanol flow rate and air flow rate on stack efficiency was studied. The results show that lower methanol flow rate, lower methanol concentration and higher air flow rate are all helpful in decreasing the methanol crossover and increase the stack faradaic efficiency.