The potential cycling of a polymer electrolyte fuel cell (PEFC) incorporating a reference electrode was carried out for 20 h. After the potential cycling, the maximum power density decreased from 56.12 mW cm(-2) of the fresh membrane electrode assembly (MEA) to 47.64 mW cm(-2). Electrochemical impedance spectroscopy (EIS) was used to conduct an independent quantitative analysis of the anode and cathode degradation. The EIS results of the anode and cathode revealed the degradation properties after the potential cycling. For the anode, the charge transfer and mass transfer resistances significantly increased after the degradation procedure, indicating that a significant degradation occurred. However, for the cathode, it was demonstrated that a slight degradation occurred, because the charge transfer and mass transfer resistances slightly increased after the degradation procedure. The increase in the charge transfer resistance was attributed to the decrease in the Pt surface area, and the increased mass transfer resistance was considered to be due to the ionomer degradation. Meanwhile, the increase in the membrane resistance and decrease in the adsorption resistance were also observed after the degradation procedure. (C) 2014 Elsevier Ltd. All rights reserved.