Fuel Cells are electrochemical cells which convert the chemical energy of a fuel (hydrogen) and an oxidizing agent (oxygen) into electricity.
Fuel cells consist of an anode, a cathode, and an electrolyte that allows ions to move between the two sides of the fuel cell. At the anode a catalyst causes the fuel to generate ions (moving from anode to cathode) and electrons (moving from cathode to anode), which creates direct current electricity. At the cathode, another catalyst causes ions, electrons, and oxygen to react forming water.
3 major types of fuel cells are most relevant today, classified by the type of electrolyte that they employ: proton exchange membrane fuel cells (PEM or PEMFC), solid oxide fuel cells (SOFC) and alkaline fuel cells (AFC).
Since each fuel cell produces only approx. 0,7 Volt, fuel cells need to be stacked in order to create the required application voltage.