This study addresses the poisoning effect of acrylonitrile (AcN) on the catalytic activity of a Pt/C catalyst modified GC disk electrode toward the oxygen reduction reaction (ORR) in O-2-saturated 0.1 M HClO4 solution. A significant retarding effect of AcN on the catalytic performance of the Pt/C catalyst toward the ORR is observed. For instance, the presence of 1 ppm AcN in solution causes a cathodic shift of the half-wave potential of the ORR by ca. 85 mV with the formation of hydrogen peroxide (2-electron reduction product of O-2). Similar Tafel slopes (close to -68 mV dec(-1)) are obtained at the unpoisoned and the poisoned Pt/C catalysts at low current density region. Whereas, a larger Tafel slope (ca. -228 mV dec(-1)) is observed at the poisoned catalyst than that obtained at the unpoisoned Pt/C catalyst (ca. -128 mV dec(-1)) at high current density region. The adsorption of AcN on the surface of the Pt/C is believed to alter its work function (Phi) in such a way that deteriorates its catalytic activity. The recovery of the performance of the Pt/C catalyst is achieved by employing a few potential cycles between the onset potentials of the hydrogen and the oxygen evolution reactions. (C) 2012 Elsevier B.V. All rights reserved.