Fuel cells are a type of electrochemical cell that convert chemical energy from a fuel into electrical energy through an electrochemical reaction. They consist of two electrodes, a cathode and an anode, separated by an electrolyte. The fuel, typically hydrogen, is fed into the anode, where it undergoes an oxidation reaction to produce protons and electrons. The protons pass through the electrolyte to the cathode, where they react with oxygen to produce water and generate an electrical current.