Simultaneous time-resolved ATR-SEIRAS and CO-charge displacement experiments: The dynamics of CO adsorption on polycrystalline Pt

The high sensitivity of ATR-SEIRAS allowed simultaneous recording of time-resolved infrared spectra of the Pt-electrolyte interface and of the current flowing during CO-charge displacement experiments. These experiments revealed the dynamics of CO adsorption on Pt, as well as of the rearrangement of the interfacial water layer. Our experiments show that COL sites are populated first, COB appearing only at slightly higher coverages. At potentials sufficiently separated from the potential of zero total charge, the charge displaced upon CO adsorption on Pt and the integrated intensity of the COL band run approximately parallel, as also do the current transient and the time derivative of the integrated intensity of the COL band. This suggests that, for low to medium CO coverage, the current flowing at a given instant during the CO-charge displacement experiment corresponds to the instantaneous rate of CO adsorption, while the charge displaced when a CO submonolayer is formed is a good estimate of the corresponding relative coverage. Although the structure of the interfacial water layer is affected at low coverages, the band corresponding to interfacial water on top of a CO-covered Pt surface only appears at a relatively high CO coverage, suggesting that this kind of interfacial water is linked to the presence of compact islands of adsorbed CO.