**1.1.1 Proton exchange membrane fuel cell (PEMFC)**

PEM fuel cell uses a solid polymer electrolyte, which is an excellent protonic conductor. In this electrolyte the ion exchange occurs between two porous electrodes. The operating temperature of the fuel cell type PEM is about 100 °C (Ellis et al., 2001).

The advantages of PEM fuel cell are its high charge density and its fast startup time, interesting features for automotive applications. The low temperature makes the technology competitive in the transportation sector and in commercial applications such as laptop computers, bicycles and mobile phones. The main disadvantages of PEM fuel cell are its low operating efficiency (40-45%) and the use of a noble catalyst such as platinum, whose CO intolerance ends up limiting the further popularization of this cell type (Farooque & Maru, 2001).

Two subcategories of PEM fuel cells are currently being widely studied, for allowing the use of other fuels other than hydrogen directly into the cell: direct methanol (DMFC) and direct ethanol (DEFC).

DMFC and DEFC fuel cells use a solid polymer electrolyte for ionic transport. However, they use, respectively, liquid methanol and ethanol as fuel instead of hydrogen. During chemical reactions, the fuel (methanol or ethanol) is directly oxidized in the anode. At the cathode, the reaction occurs with oxygen, producing electricity and water as a byproduct (Ellis et al., 2001; Garcia et al., 2004).
