Adsorption of CO at palladium monolayers deposited on Pt(111) electrodes. Combined spectroelectrochemical and theoretical study

A combined in situ spectroelectrochemical and theoretical study of CO adsor bed on clean and palladium-covered Pt(111) single-crystal electrodes is pre sented. The in situ spectra of CO adsorbed on the Pt(111) and Pd supported on Pt(111) single-crystal electrodes show different bands corresponding to the C-O stretching mode that are assigned with the help of density function al cluster model calculations. For the palladium-covered Pt(111) electrode with a palladium coverage close to the monolayer, the resulting spectra can be interpreted by using a pure Pd cluster model only. A shift to higher vi brational frequencies is observed which increases with increasing CO covera ge. This shift can be interpreted as a change in the adsorption site becaus e of coverage effects in agreement with UHV results at 300 K. The present s tudy shows that the combined use of spectroelectrochemical and first princi ples calculations is a promising and powerful tool for the interpretation o f complex electrochemical interfaces.