【正文】 between the DMFC and DBFC systems increases with respect to operation time and power output.The fuel cartridge volume of the DMFC system is smaller than that of the DBFC system (see Fig. 6). A 246ml cartridge filled with pure MeOH is needed for 10 h operation at a 20W power output, pared with a 612ml cartridge filled with 10%NaBH4–20%NaOHaqueous solution in the 8eDBFC system.. Total costs of DMFC and DBFC systems. Production costsThe production costs of typical DMFC and DBFC systems prise those of the membranes, electrodes, bipolar plates, peripherals and assembly process. In addition, the costs of ‘nonactive’ items necessary to supply, remove and treat fluids (pumps, fans, valves, humidity regulators, etc.) need to be included. It is known that the DMFC is more expensive than the DBFC, mainly due to the high costs of materials used in fabrication (especially, the platinum electrocatalysts). Furthermore, the plex cell structure required for the elimination of CO2 generated within the cell and the fuel solution concentration sensor add to the costs. Dyer [7] reported a production cost for a DMFC system as high as $5 per Watt (note, all costs in this study are given in US$).On the other hand, MERIT researchers [43] announced in 2005 that they planned to sell a 20W DBFC system for laptop puter use at a price of $90 in 2006. Considering that the standard formula to evaluate the manufacturing cost is onethird of the selling cost, this implies a fixed DBFC cost of $ per Watt or $30 for a power output of 20W. The lower production cost of DBFC might be due to its several advantages such as the use of nonPtbased electrocatalysts and a more pact cell structure.. Fuel costsThe current price of MeOH fuel for DMFCs is $ per kg [35] and of NaBH4 for DBFCs is $55 per kg. Therefore, considering the amount of the fuel consumed to generate power output, as listed in Table 3, the cost of MeOH is $ perW, while that of NaBH4 is US $ perWthe 8eDBFC system and $ per W for the 6eDBFC system.Furthermore, given the amount of fuel crossover and the power density in each fuel cell system (Table 1), the additional cost of the fuel loss is calculated to be $ per W for the DMFC and $ per W for the DBFC. Total costsConsidering the production and fuel costs in each fuel cell system, the total cost of each system can be calculated using the following equations for DMFC, 8eDBFC and 6eDBFC systems, respectively:$total,DMFC = $(Wfixed) + $(W)(h) + (W)(h) (10)$total,8eDBFC = $(Wfixed) + $(W)(h) + (W)(h) (11)$total,6eDBFC = $(Wfixed) + $(W)(h) + (W)(h) (12)In each equation, the first term is the production cost of the fuel cell system, the second is the cost of the fuel consumed for solely generating the power, and third is the cost of fuel due to crossover. In addition, Wfixed is the fixed power capacity of the fuel cell, W the power output in watts, and h is the operation time in h.The total costs of each fuel cell system operated with a power output of 20Wfor up to 3000 h are shown in Fig. 7. When using a portable device with a power output of 20Wcontinuously, the 8eDBFC system is more petitive than the DMFC system only for operation times under 280 h. Nevertheless, the petitiveness of the 8eDBFC system within this short operational timeframe has no practical potential for mercial operation due to a desired durability or lifespan of more 5000 h. Therefore at the level of current technology, it is very clear that at higher power outputs and longer operation times, the DMFC system is more petitive than the DBFC system in terms of total costs. Nevertheless, the DBFC system could be more favourable in specific application fields such as for smaller or micro power systems for which short operation times are acceptable. In addition, such miniaturized application fields also require a significant reduction in cell size, for which the DBFC remains more petitive than the DMFC.The lower petitiveness of the DBFC system in terms of total costs is primarily ascribed to the high price of NaBH4. Therefore, any reduction in the price or consumed amount of NaBH4 would make the DBFC system more petitive than the DMFC system in all portable applications. For example, at half the current price, ., $ kg?1 (NaBH4), with all other conditions held constant, the parative total cost of the systems can be calculated as presented in Fig. 8.In addition, if the NaBH4 loss due to crossover could be reduced more than that of DMFC by one order of magnitude, ., to 10?8 (mol of NaBH4 cm?2 s?1), the 8eDBFC system would bee the most petitive of the three fuel cell systems, as shown in Fig. 9. It should be possible to decrease substantially the NaBH4 crossover by increasing the power density and by developing a CEM electrolyte that is more resistant to crossover.6. ConclusionsMany factors must be considered to ascertain whether a DMFC or a DBFC is the more petitive for portable power supply systems. The present paper, first addresses some of the relative factors such as the amount or volume of consumed fuel and fuel solution, water and gases generated, and the fuel cartridge volume of each fuel cell system. The total cost of each system is then evaluated to determine the relative favourability of each fuel cell type. This analysis is based entirely on the current technologies with some generally accepted conditions being assumedAfter considering fuel crossover, the calculated amount of fuel solution (or fuel chamber volume in the anode partment) of each fuel cell necessary to generate a power output of 20Wis l in the 1MDMFCsystem and l of 10%NaBH4–20% NaOH aqueous solution in the 8eDBFC system. In addition, theDMFC system is relatively less petitive than the 8eDBFC system in terms of the amount of byproducts generated during the cell operation such aswater and gas. This result indicates that the DBFC system could be more favourable in applications thatrequire