Effect of chemisorbed carbon monoxide on Pt/C electrode on the mechanism of the hydrogen oxidation reaction

Abstract

The influence of poisoning of Pt catalyst by CO on the kinetics and mechanism of H-2 oxidation reaction (HOR) at Pt/C electrode in 0.5 mol dm(-3) HClO4, saturated with H-2 containing 100 ppm CO, was examined with rotating disc electrode (RDE) at 22 degrees C. Commercial carbon black, Vulcan XC-72 was used as support, while Pt/C catalyst was prepared by modified polyol synthesis method in an ethylene glycol (EG) solution. The kinetically controlled current (l(k)) for the HOR at Pt/C decreases significantly at CO coverage (Theta(co)) > 0.6. For Theta(co) lt 0.6 the HOR takes place through Tafel-Volmer mechanism with Tafel reaction as rate-determining step at the low CO coverage, while Volmer step controls the overall reaction rate at the medium CO coverage. When CO coverage is higher then 0.6, Heyrovsky-Volmer mechanism is operative for the HOR with Heyrovsky as the rate-determining step (rds).