Varieties of DMFCs

The electrical parameters of varieties supplied with a liquid solution are lower than those of varieties supplied with gases, but research in DMFCs has mainly been done exactly with a liquid supply. This type of cell is much simpler to design and operate, inasmuch as neither a special evaporator nor dual temperature control (for the evaporator and for the reaction zone of the fuel cell) is needed. With the supply of a liquid methanol solution, all risk of the membrane drying out close to the anode is eliminated. The elimination of heat is also easier with cells that have a liquid solution supply. All subsequent information on DMFCs in this chapter refers to the variety supplied with a liquid water-methanol solution. 

The electrical performance flgures of active DMFCs are much higher than those of passive DMFCs. Yet owing to the need to use many ancillary pieces of equipment, such as pumps, valves, and controllers, power plants with active DMFCs are much more complex and in a number of cases are less reliable in their operation. Also, part of the electrical energy generated by them is used up 

As a rule, passive fuel cell systems are simpler to operate, more reliable, and cheaper than active systems. They are used primarily for power plants with low output, such as those supplying power for portable devices. Active systems are more appropriate for power plants with higher output. 

As mentioned by Ren et al. (2000), main applications of DMFCs in the near future will be as a power supply for various portable electronic devices with civil, commercial, or military uses. In the future, power plants for electric vehicles and other transport media will join these applications. All these applications have specific features  

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