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 (theta(SnO2)) 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 theta(SnO2) was controlled by the SnCl2 concentration. The CO-stripping voltammogram of the Pt/SnO2 electrode with theta(SnO2) = 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 theta(SnO2) = 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.