Abstract
This paper describes inner-water circulation DMFC (Direct Methanol Fuel Cell) system with low water cross-over MEA (Membrane Electrode Assembly). Water permeation controlled layer which has lower permeability (K~10 -14 m 2) than conventional micro porous layer (K~10 -13 m 2) was sandwiched between anode gas diffusion layer and anode catalyst layer. This layer blocks liquid water permeation from anode gas diffusion layer to anode catalyst layer and enhances water diffusion from cathode to anode. Water flux through the membrane can be changed from anode to cathode or cathode to anode based on operation parameters (air flow rate, cell temperature, fuel pump flow rate, anode circulation pump flow rate). The effect of operation parameters for water, methanol transport through the membrane and performance were examined experimentally. With these result, system operation method to control anode methanol concentration and solution volume by manipulating flux through the membrane was analyzed. As a result, the method to control methanol concentration by fuel pump flow rate and the method to control solution volume by air pump flow rate was established. This system enabled not only to achieve higher water and methanol utilization efficiency but also increased power efficiency without extra devices for cathode water condensation and recycling. DMFC total system volume was reduced for portable uses.
