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Phosphoric Acid Fuel Cells

This system is already commercially available, with operational installations in buildings, hotels, hospitals and electric utilities. There are over 50 MW of demonstrators, worldwide, that have been tested. 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. Until the last few years, most of the funding for PAFC development had come from the U.S. gas and electric utilities. Since the establishment of the Moonlight program, in , a lot of the initial focus has shifted to Japan and its two main Utilities, Tokyo Gas and Osaka Gas. All major demonstration projects presently underway are sited in Japan. The principal use of these systems is expected to be stationary applications, because the corrosive liquid electrolyte and high temperature (160-220C) require complex system . However Sanyo makes a portable 24 V, 250 W phosphoric acid fuel cell. The system weights 60-pounds and uses pure hydrogen. A schematic description of the components in an PAFC is shown here:

The electrochemical reactions in the PAFC occur on highly dispersed electrocatalyst particles supported on carbon black. Platinum (Pt) or Pt alloys are used as the catalyst at both electrodes. Concentrated phosphoric acid is used as the electrolyte in PAFCs. At lower temperatures than 160oC, phosphoric acid is a poor ionic conductor and CO poisoning of the Pt electrocalyst on anodes becomes more severe. The use of concentrated acid, i.e. "100%, retained on a silicon carbide matrix can minimize the water vapor pressure and thus facilitate the water management of such cells.

Commercially available 200-kW PAFCs, which now cost around $3000/kW (with early sales qualifying for a $1000/kW federal subsidy), are expected to find market niches in applications under 1 MW where high-reliability service is desired and where there is a need for cogenerated low-temperature steam. The leading producer of PAFCs, International Fuel Cells, is a joint venture of Toshiba of Japan and the Hamilton Standard division of Pratt & Whitney's parent company, United Technologies Corporation. UTC has committed substantial resources to lowering installed costs for PAFCs to around $1500/kW.