In recent years, the scientists have designed the cells which convert chemical energy of a fuel directly into electrical energy. These cells are called fuel cells. These are the voltaic cells in which, the fuels such as H₂, CO, CH₄, C₂H₈ etc. are used to produce electrical energy with no the intervention of thermal devices like boiler, turbines, etc.

The conventional method of conversion of chemical energy of a fuel into electrical energy produced of a fuel to liberate heat. The heat energy so formed is used to produce steam for spinning the turbines which are joined to electrical generators. This process is approximately 40% efficient.

Fuel cells are designed to be oxidized and reduced at the electrodes are stored outside the cell and are constantly supplied to the electrodes. In fact, fuel cell is a flow battery that continues to operate as long as the reactants from outside are fed into it. One of the most successful fuel cells uses the reaction of the hydrogen and oxygen and oxygen to form water and is known as H₂ - O₂ fuel cell. The H₂ - O₂ fuel cell is also called Bacon cell after the name of its inventor and it had been used to power the Apollo space Missions. The water vapours produced during water supply for the astronauts. 

The cell consists of porous carbon electrodes and impregnated with catalyst (Pt, Ag or COO). Hydrogen and oxygen are bubbled from the electrodes into electrolyte which is an aqueous solution of NaOH or KOH.

The electrode reactions are:

 

The cell runs endlessly as long as the gases hydrogen and oxygen are supplied at the temperature 525 K and 50 atm. pressure.