500h continuous aging test on high-temperature PEMFC (phosphoric acid-doped PBI system) was conducted, steady-state performance (current density = 640 mA cm(-2)) was recorded, polarization curves were tested every 24 h, and electrochemical techniques-cyclic voltametry (CV) and electrochemical impedance spectroscopy (EIS)-were used to study the relationship between electrochemical surface area (ESA), internal resistance (R-in) and charge transfer resistance (R-ct) with time. Our research results showed that after about 100h activation, the cell performance began to degrade, and the cell voltage degradation rate is about 150 AV h(-1) at 640 mA cm(-2). AC impedance measurements showed that there was no obvious membrane degradation for internal resistance remains almost stable. The main reason for performance degradation is the decrease of ESA and the increase of Rct, which implied that obvious degradation occurs at catalyst. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.