Energetics of Oxygen Adatoms, Hydroxyl Species and Water Dissociation on Pt(111)

Calorimetric measurements of the adsorption enthalpy of gaseous oxygen (O2,g) to make two oxygen adatoms (2 Oad) on Pt(111) were performed by Fiorin et al.(1) However, we show that they used a calibration value for the optical reflectivity of Pt(111) that was incorrectly reported in the literature. This error in reflectivity led to a 40% error in the adsorption energies originally reported. We use our more accurate reflectivity of 76% to recalibrate their oxygen adsorption enthalpy data and show that it gives nearly identical results below 0.15 ML to the heats of adsorption determined from the temperature programmed desorption (TPD) experiments of two separate groups.(2, 3) Differences arise above 0.15 ML, but we attribute these to the very low sticking probability of O2,g on Pt(111) (<0.05) above 0.15 ML, which can lead to large errors in the adsorption energies measured by calorimetry. Given this, we propose that the most reliable values for the adsorption enthalpy of oxygen on Pt(111) up to 1/4 ML are ...