Two phase flow study in a direct methanol fuel cell

A three dimensional, two-phase, multi-component model has been developed for a liquid-fed DMFC. Both liquid and gas phases are considered in the entire anode, including the channel, the diffusion layer and the catalyst layer; while at the cathode, two-phases are considered in the gas diffusion layer and the catalyst layer but single gas phase is considered in the channel. For the electrochemical kinetics, the Tafel equation incorporating the effects of two phases is used at both the cathode and anode sides. At the anode side, the presence of gas phase reduces the active catalyst areas; at the cathode side, the presence of liquid reduces the active catalyst areas. The mixed potential effects due to methanol crossover are also included in the model. The modeling results showed that the porosity of the anode diffusion layer played a very important role in the DMFC performance. With a low porosity, the produced carbon dioxide cannot be removed effectively from the catalyst layer, thus reducing the active catalyst area as well as blocking methanol from reaching the reaction zone. A similar effect exits in the cathode for the liquid water. The modeling results also show that the single-phase flow models over-predict methanol cross-over.