Proton exchange membranes for direct methanol fuel cells: Properties critical study concerning methanol crossover and proton conductivity

Abstract

Generally, standard R&D procedures regarding the proton exchange membrane (PEM) development for direct methanol fuel cell (DMFC) applications do not allow direct conclusions concerning the PEM limiting characteristics. In this regard, a recent developed DMFC model is used to predict the influence of the PEM proton conductivity and permeability towards methanol on the DMFC performance. In addition, the application of the present model was performed in order to answer some open questions regarding the PEM properties for DMFC applications. The mathematical model uses as inputs membrane properties obtained from easy-to-implement standard characterization methods. From the simulation results it was verified that the PEM electrolyte and barrier properties play a decisive role on the DMFC performance. The proton conductivity seems to influence mainly the DMFC current and power density and the cell efficiency regarding fuel conversion (Faraday efficiency). On the other hand, the permeability towards methanol was found to influence all the studied DMFC outputs as it is directly related to the fuel loss and parasitic reaction of methanol in the cathode catalyst layer. As expected, the simulations show that the optimal PEM properties for DMFC applications are high proton conductivity to reduce the Ohmic losses and low permeability towards methanol in order to prevent the crossing over of methanol from the anode to the cathode.