CO adsorption kinetics and adlayer build-up studied by combined ATR-FTIR spectroscopy and on-line DEMS under continuous flow conditions

Using a novel combined spectro-electrochemical DEMS/ATR-FTIRS technique, the CO adsorption kinetics on a Pt film electrode were studied, performing transient CO adsorption experiments at different constant potentials (0.06-0.6 V). CO adsorption rate and CO_ad coverage were determined continuously from the CO consumption measured by on-line differential electrochemical mass spectrometry (DEMS). Simultaneously measured FTIR spectra, recorded in situ in an attenuated total reflection (ATR) configuration, allow a direct correlation of the IR band intensity and frequency with CO_ad surface coverage at different constant potentials. The data show that (i) the CO adsorption kinetics are independent of the adsorption potential up to 0.5 V, (ii) a significant potential dependence of the ratio between CO_L and CO_M for the same coverage, (iii) in the regime of very high CO_ad coverages there is no proportional relation between CO_ad coverage and CO_L,M intensity, and (iv) a distinct tendency for CO_ad island formation at E_ads < 0.2 V and > 0.4 V, most likely due to coadsorption of H-upd at the lower potentials and (bi-)sulfate at higher potentials. Finally, at 0.6 V, CO_ad oxidation follows a Langmuir-Hinshelwood mechanism with the highest CO₂ formation rate at a relative CO_ad coverage of ∼0.4.