A Fuel Cell converts the chemical energy of a fuel (like hydrogen) directly into electrical energy.

• In the $H_2-O_2$ fuel cell (used in the Apollo space program):

1. Anode: $2H_2+4O{H}^{-}\to 4H_{2}O+4e^{-}$
2. Cathode: $O_2+2H_{2}O+4e^{-}\to 4O{H}^{-}$

• Overall Reaction: $2H_2(g)+O_2(g)\to 2H_{2}O(l)$
• Advantages: It is highly efficient and produces only water as a byproduct, making it pollution-free.