Water and heat management of vapor-fed direct methanol fuel cells with a non-isothermal triple-phase mass transfer model

Abstract

Direct methanol fuel cells (DMFCs) operating with methanol vapor tends to operate under higher temperature, which contributes to improve cell performance and specific energy. However, the design of vapor-fed DMFCs with high performance and adaptability are still hindered by the complex water and heat management. To provide a comprehensive understanding of the critical multiphase heat and mass transfer, we develop a two-dimensional non-isothermal triple-phase mass transfer model for a passive vapor-fed DMFC. Effects of the electrochemical reactions and related thermal effect are fully investigated. Increasing the current density raises the operating temperature, thus enhancing the generation rate of methanol vapor and reducing concentration polarization under high current densities. With the enlargement of the open area ratio (from 0.1 to 0.3), an excessive methanol supply rate may cause deteriorated methanol crossover rates and excessively high temperatures, resulting in severe dehydration of polymer electrolytes and a degraded cathode overpotential (from −0.48V to −0.54V). For the DMFC with Nafion 112 membrane, the maximum current density and peak power density are 33.3% and 36.0% greater than that of Nafion 117 membrane. The simulation work will provide an exhaustive theoretical guidance for the efficient management of water and heat in DMFCs fed with neat methanol.