First-Principles Study of Rh Segregation in the Au–Rh(111) Alloy with Adsorbed NO, CO, or O2

Adsorbate-induced surface segregation significantly influences the catalytic and electrochemical performance of bimetallic alloys. Using density functional theory (DFT), we investigated Rh segregation in Au-Rh(111) alloys under the influence of adsorbed NO, CO, or O₂. The computational results reveal that these adsorbates can markedly alter Rh segregation trends on the Au-Rh(111) surface. Under vacuum conditions, the Rh atom remains preferentially in the bulk of the alloy; whereas, in the presence of adsorption, it segregates to the topmost layer, where NO has the greatest influence, followed by CO and O₂. Electronic structure analysis and adsorption energy evaluations further reveal that the strength of the surface-adsorbate interactions critically governs the Rh segregation behavior under reactive conditions. These findings establish a theoretical framework for designing Au-Rh alloys as efficient catalysts for CO oxidation.