In this paper, 550 h (500 h continuous and 50 h intermittent) high-temperature proton exchange membrane fuel cell (PEMFC, phosphoric acid-doped polybenzimidazole system, H3PO4/PBI) life test was performed without humidification at 150 degrees C; constant current (at 640 mA cm(-2)) performance and polarization curves were recorded. Electrochemical and physical characterizations were applied to investigate the degradation of the membrane electrode assembly (MEA). The results showed that the constant current performance started to reduce with a rate of 0.18 mV h(-1) after about 90 h activation. Surface area loss of the cathode platinum due to agglomeration was detected by cyclic voltammetry and transmission electron microscopy. A slight increase of internal resistance of the single cell due to H3PO4 leaching was found by electrochemical impedance spectroscopy and energy dispersive X-ray analysis. H-2 permeability of MEA increased during the last 50 h intermittent test because of appearing of cracks, that were detected by linear sweep voltammetry and scanning electron microscopy. These results suggested that catalyst agglomeration and H3PO4 leaching from catalyst layers contributed to the performance degradation of the MEA during the life test, and mechanical properties degradation of H3PO4/PBI membrane impacted badly the lifetime of the single cell. (c) 2006 The Electrochemical Society.