Effect of Liquid Barrier Layer on Open-Cathode Direct Methanol Fuel Cell Systems

Abstract

A direct methanol fuel cell (DMFC) has several advantages as a power supply for the next generation of portable electronic devices, such as laptop computers, USB chargers, and cell phones. A key feature is that the volumetric and gravimetric energy density of the fuel, liquid methanol, are much higher than those for the hydrogen fuel used in the more common types of low temperature fuel cell, proton exchange membrane fuel cells. DMFC system designs may be closed-cathode, in which water is recovered from the cathode exit for use in the anode reaction, or open-cathode, in which water is passively transported through the membrane from the cathode side to the anode. To advance the development of this technology, some inherent problems, such as methanol crossover, slow reaction kinetics, cell degradation, and water management need to be resolved. In order to reduce the water crossover rate, modifications of the membrane electrode assembly (MEA) is quite common in the literature. In the current paper, the effects of different operation parameters, such as cell temperature and current density, on the properties of an added hydrophobic liquid water barrier layer (LWBL) are presented. The results show that the polarization curve of an MEA with an LWBL drops earlier in the mass transport limitation region at higher temperature than a nominal MEA under the same conditions. One of the possible causes of this phenomenon is the competition between the water vapor and oxygen diffusion through the same passage. The water vapor transport rate though the LWBL was also experimentally determined at various operating conditions to validate the hypothesis. This work advances the understanding of the effect of a LWBL on a DMFC and contributes a framework to support the development of a control strategy to maintain water balance in a DMFC system.