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.