The oxidation of nanosized rhodium facets is investigated in the presence of a high external electric field with field ion microscopy experiments (FIM). Corresponding density functional theory (DFT) calculations were done on Rh(001), Rh(011) and Rh(111). A cross-like granular structure is obtained with FIM when the electric field is increased from 11 to 12.3 V/nm, which strongly indicates that the field promotes the oxidation of the tip. The DFT calculations confirm this scenario with a corresponding reduction of the activation barrier for oxygen incorporation into the surface of an oxide layer. (c) 2007 Elsevier B.V. All rights reserved.