We have calculated the stabilities of some reactive oxygen species (ROS) in stoichiometric bulk ceria and at the low-index (111) and (110)-surfaces, both in vacuum and in the presence of additional O2 molecules. We find that the formation of intrinsic ROS, here oxygen superoxides (O2–) and peroxides (O22–), is always endothermic at vacuum conditions and that the superoxide formation always leads to a higher formation energy than the peroxide formation. In the presence of additional O2 molecules, intrinsic peroxide formation becomes exothermic at the (110)-surface in conjunction with the formation of extrinsic superoxide ions from adsorbed O2 molecules. This coexistence of intrinsic and extrinsic ROS species is anticipated to be stable at low temperatures, and can be important for understanding the ROS chemistry for nanoceria used in low-temperature applications.
Oxygen-assisted reduction of the ceria(110) surface.
(© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)