We introduce a simple and compact fuel-cell architecture consisting of only solid channels and demonstrate its validity by developing a miniature direct formic acid fuel cell (DFAFC). The proposed architecture generates electric power while pumping the fuel and removing byproduct CO 2 without any discrete pump, gas separator, or membrane electrode assembly (MEA). The fuel pump and gas separator are embedded in the channel, as reported before, by directionally growing and venting CO 2 byproduct

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... ubbles formed inside the reaction microchannels using "virtual check valve" and microporous hydrophobic venting membrane. The new architecture further eliminates the MEA, along with the issues associated with it, by flowing one stream of fuel and electrolyte mixture in a single channel consisting of both an anode and an air-breathing cathode. The reported system obtains a supply of oxygen directly from quiescent air through a gas-diffusion cathode rather than using an oxygen tank. By eliminating all the ancillary parts, the so-called "packaging penalty," which has been hindering the miniaturization of fuel cells below the order of a centimeter, is avoided. This simple and self-standing fuel-cell unit produces 16.7 mW/cm 2 , a performance comparable to the existing bulkier DFAFCs that use external pumps, pressurized oxygen or MEA. [2011-0088]