a) Advanced fuel cell stack is 50 - 75% of total weight, b) Advanced fuel cell stack is 10 - 30% of total weight, c) Assuming drop in PFSA membrane cost by order of magnitude, d) Assuming, in each case, a 50 kW; 300 kWh system of overall weight 400 kg and overall energy conv. efficiency 40%.

Table II uses some very rough estimates to compare three other key parameters for the two systems (DMFC and reformer + RAFC): the power densities, stack materials costs and system energy densities. The stack power density for the reformate/air fuel cell may be a factor of three higher, but the stack is only 10-30% of the total weight of the system vs. 50-75% of the weight expected in the case of the DMFC. The stack materials costs per kW are projected to be four times higher for the DMFC, mainly due to the lower power density, however, the DMFC stack cost is a much larger percentage of the total systems cost. The total system energy density for a 50 kW vehicle with a range of 300 miles assuming average speed of 50 mph (80 kph) is estimated to be similar for both options, around 750 Wh/kg. These estimates are very rough, but it seems that the DMFC could become a serious candidate for transportation applications, provided the following requirements are met:

(1) Catalyst loadings are further reduced,

(2) Long term stable performances are demonstrated, and

(3) Fuel efficiencies are actually increased to the 90% level.

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