Small portable devices contain more and more functions and the lack of battery energy density becomes more serious year by year. Direct methanol fuel cells (DMFCs) are strong candidates for new portable power devices, such as future laptop computers or cellular phones, because of their potential advantages of low weight, high energy density compared to current portable power devices operating at low temperature, and simple system features. [1] Another potential use is for automobile power when used at high temperature, because methanol can be stored in its liquid phase with a high energy density, unlike gas-phase pressurized hydrogen. DMFCs use methanol as fuel by the following reactions:
The stoichiometric methanol concentration required for complete reaction of all molecules to produce protons is around 64 wt % (in solution). To create DMFCs with high energy density, an extremely low-methanol-crossover, protonconductive membrane is required.
To be able to compare the energy density between DMFCs and current Li-ion batteries, the weight or volume of the fuel cell itself must be low because fuel cells are open devices, unlike closed secondary batteries, and air can be used for the cathode reactant. DMFCs can potentially achieve 1500 Wh kg -1 at 0.5 V output; this value is 5 to 10 times larger than current Li-ion batteries.