Effect of SnO2 and Rh modifications on CO-stripping kinetics and ethanol oxidation mechanism of Pt electrode.

Tin dioxide-modified Pt electrodes with different coverages ( θ SnO 2 ) were prepared by potentiostatically depositing tin on a Pt electrode in 0.1 M H₂SO₄ solutions containing various concentrations of SnCl₂, followed by oxidizing in air. The θ SnO 2 was controlled by the SnCl₂ concentration. The CO-stripping voltammogram of the Pt/SnO₂ electrode with θ SnO 2 = 0.61 (Pt/SnO₂(0.61)) exhibited two peaks, a prepeak due to the oxidation of adsorbed CO at Pt sites adjacent to SnO₂ and a main peak due to that at Pt sites far from SnO₂. In the kinetic analysis of both peaks using CO-stripping voltammograms at various sweep rates, the rate-determining steps for the prepeak and main peak were the coupling of adsorbed CO on Pt with OH on SnO₂ surface by bifunctional effect and the dissociatively adsorption reaction of water to adsorbed OH on Pt, similar to the Pt electrode, respectively. In the linear sweep voltammograms of Pt/SnO₂ electrodes in a (0.1 M HClO₄ + 1 M ethanol) solution, the current for ethanol oxidation reaction (EOR) was the highest for θ SnO 2 = 0.61. The analysis of EOR products at different potentials for the Pt/SnO₂(0.61) electrode by in situ infrared reflectance-absorption spectroscopy exhibited the Pt/SnO₂(0.61) electrode facilitated acetic acid production. Moreover, rhodium was electrochemically deposited on the Pt sites adjacent to SnO₂ using the limited CO-stripping technique. The area-controlled Rh deposition did not change the rate-determining steps of both peaks, but it not only enhanced EOR activity, but also decreased acetic acid selectivity and increased CO₂ selectivity. [ABSTRACT FROM AUTHOR]