A fuel cell is a device that uses hydrogen or a hydrogen-rich fuel and oxygen to create an electric current. Fuel cells consist of two electrodes and an electrolyte which directly convert the chemical energy of a reaction between fuel and oxidant into electrical energy. Unlike combustion, fuel cells oxidize fuel directly into electricity without generating intermediate heat. They can achieve higher efficiency of energy conversion approaching 70% by directly converting chemical energy to electrical energy. Fuel cells consist of electrodes, electrolyte, and catalyst to facilitate the electrochemical redox reaction.