Effect of methanol

concentration on passive DMFC performance The direct methanol fuel cell (DMFC) has attracted extensive interest from scientists and engineers worldwide because its system is simple (without reformers and humidifiers), and the theoretical energy density of methanol (6100 W h/kg at 25°C) is much higher than that of gaseous fuels.[1–6] Recently, the so-called ‘passive ’ DMFC, in which external pumps or other ancillary devices for fuel and oxidant supply are removed, has been proposed and investigated.[7–14] Since passive DMFCs have much simpler structures than conventionally active DMFCs (with fuel pumps and oxidant suppliers), and the parasitic power loss from ancillary devices is eliminated, they have been considered as more promising power sources for future advanced electronic devices. Many prototypes such as toy cars,[7] cell phones[8, 9, 11] and other portable devices powered by passive DMFCs have been demonstrated. Some giant electronics companies – including Motorola, Toshiba, Samsung, NEC etc. – have also undertaken the research and development of passive DMFCs. US-based MTI MicroFuel Cells, as a lead-ing company in the commercialization of DMFCs, demonstrated several prototypes of passive DMFCs in 2001–2003, and claimed that it would enter the mass market with its own Mobion ™ technology for cell phones in 2004 or 2005.[15] [In fact MTI Micro made its first production shipment of Mobion™ technology in December 2004; see Main News (page 2) in this issue.] Presently, one of the most challenging problems for both active and passive DMFCs that employ Nafion ® membranes is methanol crossover from the anode to the cathode, which causes a mixed potential on the cath-ode and thus reduces the overall cell voltage. For this reason, one of the most important parameters that affects the performance of DMFCs is the methanol concentration, which has been widely studied. In an active DMFC with a methanol pump and an oxygen/air compressor/blower, the maximum power density can usually be achieved with 1.0–2.0 M methanol.[16, 17