Fuel cells are classified primarily on the basis of the electrolyte they use. The electrolyte is the heart of the fuel cell as it decides the important operating parameters such as the electrochemical reactions that take place in the cell, the type of catalysts required, the temperature range of cell operation, and the fuel (reactants) to be used, and therefore the applications for which these cells are most suitable. There are several types of fuel cells currently under development; a few of the most prom­ising types include

■ Polymer electrolyte membrane fuel cells (PEMFCs)

■ Direct methanol fuel cells (DMFCs)

■ Alkaline electrolyte fuel cells (AFCs)

■ Phosphoric acid fuel cells (PAFCs)

■ Molten carbonate fuel cells (MCFCs)

■ Solid oxide fuel cells (SOFCs)

■ Biofuel cells