In this paper, we evaluated the oxygen reduction reaction (ORR) activities of Pt/C, PtCo/C, and PtCoMn/C catalysts using charge- transfer resistance (Rct) and  Rct onset voltage from electrochemical impedance spectroscopy as indicators in proton exchange membrane fuel cells (PEMFC) over a wide voltage range of 0.66 V∼0.95 V.