A new class of fuel cells is being developed, based on ceramic electrolyte materials that exhibit high protonic conductivity at elevated temperatures. The protonic ceramic fuel cell (PCFC) is fundamentally different and unique among fuel cell types currently being developed because it relies on conduction of protons through the electrolyte at much higher temperatures than is possible with other proton-conducting fuel cells. Operating at 750 degreesC, the PCFC is ideal for use with hydrocarbon fuels, such as natural gas. Proton conduction implies that water vapor is produced at the cathode, where it is swept away by air, rather than at the anode (as in a solid oxide fuel cell), where it dilutes the fuel. Since carbon dioxide is the only exhaust gas produced, higher fuel utilization is possible. Ambipolar steam permeation from the cathode to the anode provides. the steam for direct reforming of hydrocarbons, so external steam injection is not required. Therefore, high thermodynamic efficiency is achieved and coking is not a problem. All of these features make it possible to construct a fuel cell of unprecedented electrical efficiency when operated on hydrocarbon fuels. The principles of operation and the current status of single-cell testing on methane at Protonetics will be described. (C) 2003 Elsevier Science B.V. All rights reserved.