Oxygen Adsorption and Water Formation on Co(0001)

Abstract

Oxygen adsorption and removal on flat and defective Co(0001) surfaces have been investigated experimentally using scanning tunneling microscopy, temperature-programmed and isothermal reduction, synchrotron X-ray photoemission spectroscopy, and work function measurements under ultrahigh vacuum conditions and H2/CO pressures in the 10–5 mbar regime. Exposure of the Co(0001) to O2(g) at 250 K leads to the formation of p(2 × 2) islands with a local coverage of 0.25 ML. Oxygen adsorption continues beyond 0.25 ML, reaching a saturation point of ∼0.39 ML Oad, without forming cobalt oxide. Chemisorbed oxygen adlayers can be reduced on both flat and defective Co(0001) surfaces by heating in the presence of ∼2.3 × 10–5 mbar H2(g). The onset of the oxygen removal as water during temperature-programmed reduction experiments (1 K s–1) is at around 450 K on flat Co(0001) and 550 K on defective Co(0001). By evaluation of isothermal reduction experiments using a kinetic model, the activation energy for water formation is...