Water structures at electrolyte/electrode interfaces are crucial for electrochemical reaction selectivity and kinetics. This study uses scanning tunneling microscopy (STM) and noncontact atomic force microscopy (AFM) to visualize alkali metal cation-containing water layers on a charged Au(111) surface with atomic resolution. Li⁺ cations are elevated from the surface, forming an ice-like water layer, while K⁺ and Cs⁺ cations are in direct contact. The water network structure transitions from hexagonal (Li⁺) to distorted hydrogen-bonding (Cs⁺). Surface-enhanced infrared absorption spectroscopy (SEIRAS) data supports these findings, suggesting significant alkali metal cation impacts on hydrogen evolution reaction (HER) kinetics and efficiency. These insights highlight the critical role of spectator ions in electrochemical processes.
