Water-neutral micro direct-methanol fuel cell (DMFC) for portable applications

Abstract

Water loss and water recycling in direct-methanol fuel cells (DMFCs) is a major issue that affects the complexity, volume and weight of the system and becomes of greater concern as the size of the DMFC decreases. Flat micro DMFCs were built in a plastic housing with a water-management system that controls the flux of liquid-water through the membrane and the loss of water during operation. These cells contain a nanoporous proton-conducting membrane (NP-PCM). Methanol consumption and water loss were measured during operation in static air at room temperature for up to 900 h. Water flux through the membrane varied from negative, through zero, to positive values as a function of the thickness and the properties of the water-management system. The loss of water molecules (to the air) per molecule of methanol consumed in the cell reaction (defined as the W factor) varied from 0.5 to 7. When W equals 2 (water flux through the membrane equals zero) there is no need to add water to the DMFC and the cell is operating under water-neutral conditions. When W is smaller than 2, water must be removed from the cell and when it is larger than 2, water must be added. The cell showed stable operation up to 900 h and its maximum power was 12.5 mW/cm 2.