The kinetics of the oxygen reduction reaction (ORR) on nanostructured thin-film (NSTF) ternary PtCoMn catalyst was investigated in 50 cm(2) proton-exchange membrane single cell fixtures. The investigation covered a wide range of oxygen partial pressures (0.2-0.5 atm), temperatures (30-90 degrees C), relative humidities (25-100%), and Pt loadings (0.05-0.2 mg cm(-2)) in the cathode catalyst. The kinetic data were derived from cell polarization curves measured during Galvanodynamic scans from near open-circuit to a high current density and back to near open-circuit. The kinetic data were correlated with a single Tafel equation and a transfer coefficient that is a function of the relative humidity (RH). The correlation indicates a 0.36 order for the O-2 partial pressure, 39.5 kJ mol(-1) activation energy for the temperature dependence, and an additional 0.9 order for RH dependence. The calculated mass activities and specific activities at 0.9 V Ohmic resistance corrected cell voltage, 1 atm H-2 and O-2 partial pressures, 80 degrees C and 100% RH agree well with the measured values of 0.13-0.25 A mg(pt)(-1) and 1.7-2.0 mA cm(pt)(-2) for the cells with different Pt loading. Published by Elsevier B.V.