The phosphoric acid fuel cell (PAFC) is the only fuel cell technology that is in commercialization. There are over 75 MW of demonstrators, worldwide, that have been tested, are being tested, or are being fabricated. Phosphoric acid fuel cells (PAFCs) operate at temperatures of 200°C, using molten H3PO₄ as an electrolyte.

The PAFC has been developed mainly for the medium-scale power generation market, and 200 kW demonstration units have now clocked up many thousands of hours of operation. However, in comparison with the two low temperature fuel cells, alkaline and proton exchange membrane fuel cells (AFCs, PEMFCs), PAFCs achieve only moderate current densities.

Most of the plants are in the 50 to 200 kW capacity range, but large plants of 1 MW and 5 MW have been built. The largest plant operated to date achieved 11 MW of grid quality ac power. Major efforts in the U.S. are concentrated on the improvement of PAFCs for stationary, dispersed power plants and on-site cogeneration power plants. The major industrial participants are UTC Fuel Cells in the U.S. and Fuji Electric Corporation, Toshiba Corporation, and Mitsubishi Electric Corporation in Japan.