Influence of Metallic Surface Heterogeneity on Adsorption Dynamics and Orientation of Sulfonyl-Functionalized Ionic Liquids

Ionic liquids are promising interfacial modifiers in catalysis and electrochemistry, yet their adsorption mechanisms on alloyed surfaces remain poorly understood. Here, we combine replica exchange molecular dynamics (REMD) with density functional theory (DFT) to probe the adsorption of the sulfonyl-based ionic liquid [BMP][TFSI] on two bimetallic surfaces, Au-Pt-Pt(111) and Pt-Au-Au(111), and comparisons were made with corresponding Pt(111) and Au(111) monometallic surfaces. Across all systems, adsorption is dominated by physisorption but its strength is highly sensitive to the identity of the top-layer atoms. The Pt-Au-Au(111) surface exhibits the strongest binding, driven by enhanced electrostatics with exposed platinum, while top-layer gold-rich surfaces show weaker interactions. Conformational preferences of the ions remain robust, whereas projected density of states and d-band analyses reveal that alloying-induced electronic shifts mirror adsorption trends. These results highlight the decisive role of surface composition in modulating ionic liquid organization, providing principles for tailoring functional interfaces.