The surface energy phase diagrams of CO adsorption on the low index iridium surfaces and the morphology of iridium nanoparticles

Abstract

The stability of molecular CO over the unreconstructed low-index surfaces was studied using ab initio atomistic thermodynamics. Results for Ir(100) in a diluted CO environment indicated that the 0.5 ML-phase was the most stable structure, whereas, in a concentrated CO medium, a 0.75 ML-phase exhibited the highest stability. Results of CO/Ir(110) systems indicated the presence of three stable configurations at 0.5, 0.75, and 1.0 ML, which are in agreement with reported experimental findings. Additional results revealed that among all CO/Ir(111) systems, the most stable structures were at 0.38, 0.44, and 0.81 ML coverages of CO. Shapes of Ir nanoparticles were predicted at different values of CO chemical potential using the Wulff construction. A truncated-tetrahedron shape was obtained for nanoparticles at low CO chemical potential values due to contributions of (100) and (111) facets. On the other hand, a cubic shape was obtained for nanoparticles at large CO chemical potential values. This was attributed to the sole contributions of the (100) surface to the Wulff construction.