Hydration at Highly Crowded Interfaces

Understanding the molecular and electronic structure of solvated ions at surfaces requires an analysis of the interactions between the surface, the ions, and the solvent environment on equal footing. Here, we tackle this challenge by exploring the initial stages of Cs+ hydration on a Cu(111) surface by combining experiment and theory. Remarkably, we observe inside-out solvation of Cs+ ions, i.e., their preferential location at the perimeter of the water clusters on the metal surface. In addition, water-Cs complexes containing multiple Cs+ ions are observed to form at these surfaces. Established models based on maximum ion-water coordination and conventional solvation models cannot account for this situation, and the complex interplay of microscopic interactions is the key to a fundamental understanding.

Automated summary

Understanding the molecular and electronic structure of solvated ions at surfaces requires analyzing the interactions between the surface, ions, and solvent environment. Combining experiment and theory, we investigate the initial stages of Cs+ hydration on a Cu(111) surface and observe inside-out solvation of Cs+ ions at the perimeter of water clusters on the metal surface. Additionally, water-Cs complexes containing multiple Cs+ ions are formed. Established models based on ion-water coordination and conventional solvation cannot explain this, highlighting the importance of understanding the complex microscopic interactions.