A single proton exchange membrane fuel cell (PEMFC) and associated hardware were designed for high- temperature membrane electrode assembly (MEA) testing and diagnosis in the range of 160 - 300 degrees C. The fuel cell heating strategy and its design considerations with respect to heat balance are also discussed in this paper. The fuel cell performance of PEMEAS H3PO4- doped polybenzimidazole (PBI)- based MEAs and the corresponding ac impedance diagnosis demonstrated that this single cell and its associated hardware designs are feasible for high-temperature MEA testing. The apparent exchange current densities for the cathodic oxygen reduction reaction as a function of temperature were obtained through ac impedance measurement. Rapid performance degradation was observed at extreme temperatures, such as 300 C, suggesting an accelerated fuel cell testing method. AC impedance results showed that the activity loss of the catalyst/ catalyst layer was responsible for this degradation. (c) 2007 The Electrochemical Society.