The ability to distinguish surface atoms with different coordination numbers is of fundamental importance in many fields of materials science, ranging from magnetism to heterogeneous catalysis. In this study, we exploited the capability of high-resolution core-level photoelectron spectroscopy in combination with density functional theory-based calculations to investigate this kind of atomic configurations. The measurement of the 4f7/2 core level of the (111), (100), (110), (311), and (510) surfaces allowed us to highlight the differences between surface atoms with different coordination, also related to surface reconstruction processes, atomic diffusion, and morphological changes. The shifts in core levels were correlated with the modification of the effective coordination number, which takes into account the role of the variability in the Ir-Ir interatomic distances, and with the variations in the centroids of the projected d-band ΔBd, a quantity in turn related to chemical reactivity. Besides solid surfaces, the results may aid in understanding the properties of Ir nanoparticles whose active sites on nanofacets, such as edges, corners, and steps, are of paramount relevance in heterogeneous catalysis, especially in the electrocatalytic oxygen evolution reaction.
