The Cell
In contrast to indirect methanol fuel cells, where methanol is reacted to hydrogen by steam reforming, DMFCs use a methanol solution (usually around 1M, i.e. about 3% in mass) to carry the reactant into the cell; common operating temperatures are in the range 50–120 °C, where high temperatures are usually pressurized. DMFCs themselves are more efficient at high temperatures and pressures, but these conditions end up causing so many losses in the complete system that the advantage is lost; therefore, atmospheric-pressure configurations are currently preferred.
Because of the methanol cross-over, a phenomenon by which methanol diffuses through the membrane without reacting, methanol is fed as a weak solution: this decreases efficiency significantly, since crossed-over methanol, after reaching the air side (the cathode), immediately reacts with air; though the exact kinetics are debated, the end result is a reduction of the cell voltage. Cross-over remains a major factor in inefficiencies, and often half of the methanol is lost to cross-over.
Other issues include the management of carbon dioxide created at the anode, the sluggish dynamic behavior, and the ability to maintain the solution water.
The only waste products with these types of fuel cells are carbon dioxide and water.
Read more about this topic: Direct Methanol Fuel Cell
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