**4.2 Fuel cell**

In a fuel cell, the fuel (hydrogen, natural gas, methanol, ethanol, etc.) is electrochemically oxidized at the anode, whereas the oxidant (oxygen from the air) is reduced at the cathode. Because of difficulties involved in the production, storage, and distribution of hydrogen, the use of alcohols (methanol, ethanol, etc.) as hydrogen carrier is preferred and the resulting cell is called as the direct alcohol fuel cell (DAFC). Thus, the overall efficiency of a DAFC depends upon the efficiencies of both the electrode reactions (e.g. alcohol oxidation and oxygen reduction). The mechanism of oxygen reduction reaction (ORR) is very complex. The most accepted mechanisms in acid media are, the direct four electron pathway (O2 + 4H+ + 4e- ↔ 2H2O, Eº = 1.229 VSHE) and a series two-electron pathway (O2 + 2H+ + 2e- ↔ H2O2 + 2H+ + 2e- ↔ 2H2O). The ORR and Methanol/Ethanol oxidation reaction (MOR/EOR) are traditionally catalyzed by Pt or Pt-based alloys dispersed on high surface area carbon support materials.

PPy has been investigated as carbon-substitute supports for fuel cell catalysts. Polymersupported metal particles present the higher specific surface area and the higher tolerance to poisoning due to the adsorption of CO species, in comparison to the serious problem of poisoning of bulk and carbon supported metals. Moreover conducting polymers are not only electron conducting, but also proton conducting materials, so they can replace Nafion in the catalyst layer of the fuel cell electrode and provide enhanced performance also.
