Direct methanol fuel cell is a promising candidate for portable applications since its fuel is in the liquid state at low temperatures, allowing for an energy dense and inexpensive fuel that can easily be stored. Nonetheless, the problem of methanol crossover, which is from anode to cathode is one of the main problem for commercialization of this fuel cell. In order to prevent this methanol crossover, Kordesch proposed the flowing electrolyte concept, whereby the anode and cathode are separated by a flowing liquid electrolyte, such as diluted sulfuric acid. This concept is known as the flowing electrolyte – direct methanol fuel cell or FE-DMFC. By means of this concept, the methanol, which tries to reach to the cathode side can be blocked by the flowing electrolyte channel, which nearly prevents this electrochemical short circuit. Many researchers have modelled this type of fuel cell; however the majority of studies included a single phase model and examined the performance of the FE-DMFC under different operating conditions. Recently a two-phase model of the FE-DMFC has been developed using a single-domain formulation of the multiphase mixture model (MMM) and two phase non-isothermal model which was extended the single domain as two-dimensional. Owing to the more realistic modeling predictions of the multiphase model, the single domain formulation is extended to account for 3D within the FE-DMFC. This three-dimensional and two phase model is first used to investigate the concentration distribution of methanol and saturation at the baseline condition. Then, the effect of FEC thickness is investigated for four different values of FEC thicknesses at 0.5 V cell voltage. The results show that FEC thickness should be 0.4 mm for the given set of data. At this thickness, the negative effects of methanol crossover are minimized and the power density is maximized. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 661579. Project Name: Development of a High Performance Flowing Electrolyte-Direct Methanol Fuel Cell Stack Through Modeling and Experimental Studies Acronym: FEDMFC Publication date: 2017-05-17