Poisoning Effect of Selected Hydrocarbon Impurities on the Catalytic Performance of Pt/C Catalysts towards the Oxygen Reduction Reaction

This study addresses the oxygen reduction reaction (ORR) at a typical carbon supported Pt (Pt/C) catalyst in the presence of some hydrocarbon impurities. The activity of Pt/C catalyst decreases in the presence of a few ppm concentrations of impurities (vinyl acetate (VA) > propionic acid (PA) > toluene (Tol) > triethyl amine (TEA)) in 0.1 M HClO 4 solution, as revealed by a negative shift in the half-wave potential of the ORR together with the formation of H 2 O 2 . Tafel plots for the ORR with similar slopes were obtained at the unpoisoned and the poisoned Pt/C catalysts indicating that the ORR proceeds via a similar rate-determining step (albeit with a lower kinetic current). The increase of %H 2 O 2 at the poisoned Pt/C catalyst indicates that the hydrocarbon impurities act as site-blocking species which decreases the number of active sites necessary for the favorable parallel adsorption of O 2 molecules to affect a 4-electron ORR. The order of activity loss by the hydrocarbon impurities is in line with the dipole moment of each molecule. The recovery of the catalytic activity of the poisoned Pt/C catalysts is achieved by employing a few potential cycles between the onset potentials of hydrogen and oxygen evolution reactions.