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Direct Methanol Fuel Cells (DMFCs) have been considered for use in transportation applications due to low system complexity. When providing current, methanol is electrochemically oxidized at the anode electrocatalyst to produce electrons which travel through the external circuit to the cathode electrocatalyst where they are consumed together with oxygen in a reduction reaction. The circuit is maintained within the cell by the conduction of protons in the electrolyte. In modern cells, electrolytes based on proton conducting polymer electrolyte membranes (e.g., Nafion™) are often used, since these allow for convenient cell and for high temperature and pressure operation. A schematic description of the components in a DMFC is shown here:
For an overall reaction:
2 CH3OH + 3 O2 --> 2 CO2 + 4 H2O
The heart of the direct methanol fuel cell is the proton exchange membrane: a thin membrane covered on both sides with a sparse layer of platinum-based catalyst and sandwiched between two electrodes. A methanol/water solution is introduced to a negatively charged electrode that spontaneously reacts by breaking the methanol molecules apart. Once broken up, the carbon atom combines with the oxygen atoms from the methanol and water at the negative electrode to form carbon di.
The hydrogen atoms are further divided, while the protons pass through the membrane to the positively charged electrode. Meanwhile, the hydrogen electrons are forced to go around the membrane forming an electric current. The two parts of the hydrogen atom are reunited at the positive electrode, and combined with oxygen to produce water. Because it readily frees its hydrogen to react in the fuel cell, methanol is an ideal hydrogen carrier.
