Direct-methanol fuel cell
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Direct-methanol fuel cells or DMFCs are a subcategory of Proton-exchange fuel cells where, the fuel, methanol, is not reformed, but fed directly to the fuel cell.
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[edit] Advantages
Because methanol is fed directly into the fuel cell, complicated catalytic reforming is unneeded, and storage of methanol is much easier than that of hydrogen because it does not need to be done at high pressures and (or) low temperatures, as methanol is a liquid. The energy density of methanol (the amount of energy released by using a given volume of methanol) is orders of magnitude greater than even highly compressed hydrogen.
[edit] Issues
However, efficiency is low, due to the high permeation of methanol through the membrane, and the dynamic behaviour is sluggish. Methanol is also poisonous.
At the current level of the technology, DMFCs are limited in the power they can produce, but can still store much energy in a small space. This means they can produce a small amount of power over a long period of time.
This makes DMFCs ill-suited for automotive applications although the power characteristics are appropriate for consumer goods such as cell-phones or laptops.
[edit] Reaction
The DMFC relies upon the oxidation of methanol on a catalyst layer to form carbon dioxide. Water is consumed at the anode and is produced at the cathode. Protons (H+) are transported across the proton exchange membrane to the cathode where they react with oxygen to produce water. Electrons are transported via an external circuit from anode to cathode providing power to external devices.
The half reactions are:
Anode: CH3OH + H2O → CO2 + 6H+ + 6e-
Cathode: 1.5O2 + 6H+ + 6e- → 3H2O
Net reaction: CH3OH + 1.5O2 → CO2 + 2H2O
Because water is consumed at the anode in the reaction, pure methanol cannot be used without provision of water via either passive transport such as back diffusion (osmosis), or active transport such as pumping. The need for water limits the energy density of the fuel.
[edit] History
As of 2005, the record for the smallest commercially available fuel cell is held by Toshiba, at 22 x 56 x 4.5 millimeters. This device outputs 100 milliwatts at 10 hours per milliliter of fuel, and takes advantage of new technology allowing the use of undiluted (99.5%) methanol.
| Fuel Cells |
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| Types: AFC | BE | DBFC | DEFC | DMFC | EGFC | FAFC | MCFC | MFC | MHFC | PAFC | PCFC | PEC | PEMFC | RFC | rfc | SOFC | ZFC |
| Other: Hydrogen Economy | Hydrogen storage | Hydrogen station | Hydrogen Vehicles |
