A quantitative research on S and SO2 poisoning Pt/Vulcan carbon (Pt/VC) catalysts for fuel cells was conducted by the three-electrode method. Pt/VC electrodes were contaminated by submersion in a SO2-containing solution made up of 0.2 mM Na2SO3 and 0.5 M H2SO4 for different periods of time, and held at 0.05 V (vs. RHE) in 0.5 M H2SO4 solutions in order to gain zero-valence sulfur (S-0) poisoned electrodes. The sulfur coverage of Pt was determined from the total charge consumed as the sulfur was oxidized from S-0 at 0.05 V (vs. RHE) to sulfate at >1.1 V (vs. RHE). The summation of initial coverage of S-0 (theta(S)) and coverage of H (theta(H)) are approximately equal to 1 (theta(H) + theta(S) = 1) when 0.5 < theta(H) < 1, which gives an easy way to figure out the quantity of sulfur adsorbed on Pt/VC. As to SO2 poisoned Pt/VC, the catalytic activity of oxygen reduction reaction (ORR) decreases linearly with the amount of SO2 adsorbed on the Pt nanoparticles when 0.45 < theta(H) < 0.81. When the adsorbed SO2 was reduced to S-0 the mass activity was greatly recovered, and the area specific activity was even higher than the unpoisoned Pt/VC. (C) 2012 Elsevier Ltd. All rights reserved.