The performance of a proton exchange membrane fuel cell (PEMFC) with Pd-Pt-Ni as an oxygen reduction reaction catalyst has been evaluated and analyzed with operation time using current-voltage polarization, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The cell performance increases continuously in the whole current density range with the cell operation time, but the rate of increase slows down gradually and the performance becomes constant on the seventh day. The invariable membrane resistance and the continually decreasing charge transfer resistance as indicated by the EIS data illustrate that the enhanced interfacial kinetics at the cathode contributes to the cell voltage increase. CV data reveal that the electrochemical active surface area decreases, while the catalyst surface changes from Pd-enrichment to Pt-enrichment and the peak potential for surface oxide stripping shifts positively due to metal dissolution, with operation time. The latter serves as the origin for the enhancement in catalytic activity and the overall cell performance. With the Pt-mass activity and specific activity improvement, respectively, by factors of 1.8 and 1.9 compared to commercial Pt, the Pd-Pt-Ni alloys are promising cathode catalysts for PEMFC. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3519246] All rights reserved.