A quantitative research on S- and SO 2 -poisoning Pt/Vulcan carbon fuel cell catalyst

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 0.2mM Na2SO3 and 0.5M H2SO4 for different periods of time, and held at 0.05V (vs. RHE) in 0.5M H2SO4 solutions in order to gain zero-valence sulfur (S0) poisoned electrodes. The sulfur coverage of Pt was determined from the total charge consumed as the sulfur was oxidized from S0 at 0.05V (vs. RHE) to sulfate at >1.1V (vs. RHE). The summation of initial coverage of S0 (θS) and coverage of H (θH) are approximately equal to 1 (θH+θS=1) when 0.5<θH<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<θH<0.81. When the adsorbed SO2 was reduced to S0, the mass activity was greatly recovered, and the area specific activity was even higher than the unpoisoned Pt/VC.