Direct dimethyl-ether fuel cell

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Recently, a direct methanol fuel cell (DMFC) using polymer electrolyte fuel cell (PEFC) has received much attention for small portable power sources. A drawback of the DMFC is too much permeation of methanol through a polymer electrolyte membrane (PEM) which reduces fuel efficiency and the cell performance. In 1998, we demonstrated the first direct DME (dimethyl-ether) fuel cell (DDFC), the performance of which was almost equal to that of the DMFC. The permeation properties of the DDFC and their related phenomena are studied and compared with those of DMFC in this report.1. The permeability coefficient of DME through a PEM was about one-tenth as small as that of methanol within temperature range from 60 to 80 ℃ under relative humidity of 95%.2. The fuel cross leak of operating DDFC was about one-tenth as small as that of operating DMFC. The same phenomena were observed on the DDFC as were observed on the DMFC. They were fuel permeation by diffusion, electro-osmotic permeation, and decrease of permeation due to fuel consumption in the anode catalyst layer. Farady coefficient of more than 90% was attained by DDFC.3. DME solubility in water is 5.3wt% at 20℃ and O.83wt% at 80℃4. When Pt-Ru catalyst is used on the anode, abnormal low performance of the DDFC is observed. Decomposition species from the DDFC and absorbed CO quantity on the catalyst are examined, but the origin of this abnormal phenomenon is still unknown.