An electrochemical cell that produces electricity from a replenishable fuel tank. The electricity is generated through the reaction, triggered in the presence of an electrolyte, between the fuel (on the anode side) and an oxidant (on the cathode side). The reactants flow into the cell, and the reaction products flow out of it, while the electrolyte remains within it. Fuel cells can operate virtually continuously as long as the necessary flows are maintained.
Fuel cells are different from conventional electrochemical cell batteries in that they consume reactant from an external source, which must be replenished ? a thermodynamically open system. By contrast, batteries store electrical energy chemically and hence represent a thermodynamically closed system.
Many combinations of fuels and oxidants are possible. A hydrogen fuel cell uses hydrogen as its fuel and oxygen (usually from air) as its oxidant. Other fuels include hydrocarbons and alcohols. Other oxidants include chlorine and chlorine dioxide.