Potential-dependent CO Adsorption On A Smooth Surface of Crystalline Pt By The Use of PEM-FTIR

Abstract

The potential-dependent CO adsorption in both H2 adsorption/desorption region and double layer region on polycrystalline platinum at room temperature and the oxidation of the adsorbed CO have been systemically studied. PEM-FTIR (Photon Elastic Modulation FTIR) technique along with cyclic voltammetry was used to understand the adsorption state and the mechanism of CO oxidation. In the hydrogen adsorption- desorption region of the smooth platinum surface, three types of adsorption states were observed for the CO adsorption. These states include a small portion of CO-I (Epeak =~0.75V), CO-II (Epeak=0.85~0.9V), and CO-III (Epeak=0.9V~0.95V). The CO stripping data suggest that the CO-I bonding state was kinetically least stable. In the double layer region, only CO- II or CO-III state was observed. In addition, the CO-III state was found to have much stronger bond with Pt. These results are in also in good agreement with the reported literature. The CO adsorbed in the hydrogen adsorption-desorption and double layer regions produced similar CO stretching frequency- potential slope of about 15 cm-1/V. An extended stark effect was observed for the CO adsorbed in the double layer region, indicating that CO adsorbed in double layer region is less subjected to the influence of dipole-dipole enhancement effect. The stark effect of CO adsorbed at different potentials may provide valuable information in understanding the CO oxidation mechanism.