| TECHNOLOGY |
DMFCs may also stack up well to Li-ion batteries on a size basis. One of the keys to drawing a lot of energy out of methanol in DMFCs is to use neat (pure) alcohol. But in practice, that's tough to do, he says, because concentrated methanol permeates quickly through the widely used Nafion-type membranes and reacts with oxygen at the cathode catalyst layer without producing electricity. But since PEM-style direct methanol fuel cells have many desirable attributes, they're generally run on dilute (about 3%) aqueous methanol solutions to alleviate excessive fuel leakage--even though the fuel's energy capacity is reduced. Neat methanol can be diluted on-the-fly in DMFCs by using sensors, water recirculation loops, and clever engineering, but that type of design is complex, costly, and not easily miniaturized to pocket-pager size. Worse still, it consumes much of the power produced by the fuel cell. But now there may be a way around the fueling problem for miniature fuel cells. Co.has just succeeded in operating a DMFC with neat methanol without adjusting the fuel concentration at the anode with pumps. Until now, such "passive" fueling in miniature cells required a prediluted fuel source. Based on the latest results, it's reasonable to claim that DMFCs will be able to outperform today's Li-ion batteries, in terms of energy density per volume, by a factor of three or four. Co. isn't yet ready to tell how. For now, Co. asserts that "it requires modifying more than just one component in a direct methanol fuel cell." Co. has not come up with the long-sought "super-revolutionary" membrane, he adds.
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