Direct Use of Methanol in Fuel Cells

Methanol can be nsed as one possible replacement for conventional motor fuels. The use of methanol as a motor fuel received attention during the oil crises of the 1970s due to its availability and low cost. Methanol is an attractive fuel it is hquid at room temperature, it has limited toxicity, high energy density, and is an inexpensive energy source (Shukla et al., 1998). Methanol is a favored fuel as it has twice the energy density of liquid hydrogen and since it is a liquid at normal ambient temperatures and it can thus be stored and transported easily and inexpensively (Collins, 2001). 

A relatively new member of the fuel cell family, the DMFC is similar to the PEM cell in that it uses a polymer membrane as an electrolyte. The DMFC is a special form of low-temperature fuel cell. It can be operated at 355 75 K temperatures depending on the fuel feed and type of electrolyte used. In a DMFC, methanol is fed directly into the fuel cell without the intermediate step of reforming the alcohol into hydrogen (Collins, 2001). 

The DMFC, based on a polymer electrolyte fuel cell (PEFC), uses methanol directly for electric power generation and promises technical advantages for power trains. The fuel can be delivered to the fuel cell in a gaseous or liquid form. The actual power densities of a DMFC are clearly lower than those of a conventional hydrogen-fed polymer electrolyte fuel cell. In addition, methanol permeates through the electrolyte and oxidizes at the cathode. This results in a mixed potential at the cathode (Hohlein et al., 2000). 

Methanol is one of the few alcohols that can be fed directly into a fuel cell and can be converted electrochemically at the anode. The DMFC can be fed with a gaseous or liquid fuel feed. The liquid DMFC generally uses a diluted methanol in water mixture (ty pically 1-2 molar) and only a fraction of the methanol is used at the anode (Collins, 2001). The DMFC, like an ordinary battery, provides DC electricity according to the following half reactions. 

Methanol is oxidized to CO with half reaction at the anode CHjOH + H,0 COj + 6H + 6e 

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