This study investigates the effect of ion-specific water structures at metal surfaces on hydrogen production. Using scanning tunneling microscopy (STM) and noncontact atomic force microscopy (AFM), the researchers visualize water layers containing alkali metal cations on a charged Au(111) surface at atomic resolution. They find that Li⁺ cations are elevated from the surface, facilitating the formation of an ice-like water layer between the Li⁺ cations and the surface. In contrast, K⁺ and Cs⁺ cations are in direct contact with the surface. The water network structure transitions from a hexagonal arrangement with Li⁺ to a distorted hydrogen-bonding configuration with Cs⁺. These observations are consistent with surface-enhanced infrared absorption spectroscopy data and suggest that alkali metal cations significantly impact hydrogen evolution reaction kinetics and efficiency. The microscopic structure of the electrical double layer (EDL) between the electrode and electrolyte plays a crucial role in determining the selectivity and kinetics of electrochemical reactions. The Gouy–Chapman–Stern (GCS) model is the predominant framework for describing the EDL, which encompasses a Stern layer and a diffuse layer. However, this model, rooted in classical mean-field theory, overlooks the specific water orientation and ion arrangement at the molecular scale. Therefore, it struggles to interpret phenomena such as ion-specific effects, overcharging, and water orientational asymmetry. Alkali metal cations have been found to alter the interfacial solvation environment and electrochemically active sites, which in turn impact the proton-coupled electron-transfer (PCET) barrier in hydrogen evolution reaction (HER)/hydrogen oxidation reaction (HOR) and the mass transport processes of oxidation reactions, varying with the different cations present. The study explores molecular-level details of the EDL from both experiment and theory, remaining a formidable challenge. Various vibration spectroscopy and diffraction techniques have been employed to identify the EDL structure at electrode/electrolyte interfaces. Recent advancements in surface-enhanced vibrational spectroscopy, including surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRAS), have enabled researchers to discern the dipole orientation and H-bonding structure of water molecules near the electrified interface. However, these techniques endure poor spatial resolution and the difficulty of spectral assignment. Recently, individual Na⁺ hydrates, hydronium-water layers and alkali ion-water chains were successfully visualized by noncontact atomic force microscopy (AFM) with a carbon monoxide (CO)-terminated tip. This development opens up the possibility of probing interfacial ion-water interactions with atomic precision. In this work, the researchers investigated the extended network formed by different alkali metal cations and water molecules on a charged Au(111) surface in real space, which constitutes an ideal model system to understand the atomic structure at electrolyte/electrode interfaceThis study investigates the effect of ion-specific water structures at metal surfaces on hydrogen production. Using scanning tunneling microscopy (STM) and noncontact atomic force microscopy (AFM), the researchers visualize water layers containing alkali metal cations on a charged Au(111) surface at atomic resolution. They find that Li⁺ cations are elevated from the surface, facilitating the formation of an ice-like water layer between the Li⁺ cations and the surface. In contrast, K⁺ and Cs⁺ cations are in direct contact with the surface. The water network structure transitions from a hexagonal arrangement with Li⁺ to a distorted hydrogen-bonding configuration with Cs⁺. These observations are consistent with surface-enhanced infrared absorption spectroscopy data and suggest that alkali metal cations significantly impact hydrogen evolution reaction kinetics and efficiency. The microscopic structure of the electrical double layer (EDL) between the electrode and electrolyte plays a crucial role in determining the selectivity and kinetics of electrochemical reactions. The Gouy–Chapman–Stern (GCS) model is the predominant framework for describing the EDL, which encompasses a Stern layer and a diffuse layer. However, this model, rooted in classical mean-field theory, overlooks the specific water orientation and ion arrangement at the molecular scale. Therefore, it struggles to interpret phenomena such as ion-specific effects, overcharging, and water orientational asymmetry. Alkali metal cations have been found to alter the interfacial solvation environment and electrochemically active sites, which in turn impact the proton-coupled electron-transfer (PCET) barrier in hydrogen evolution reaction (HER)/hydrogen oxidation reaction (HOR) and the mass transport processes of oxidation reactions, varying with the different cations present. The study explores molecular-level details of the EDL from both experiment and theory, remaining a formidable challenge. Various vibration spectroscopy and diffraction techniques have been employed to identify the EDL structure at electrode/electrolyte interfaces. Recent advancements in surface-enhanced vibrational spectroscopy, including surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRAS), have enabled researchers to discern the dipole orientation and H-bonding structure of water molecules near the electrified interface. However, these techniques endure poor spatial resolution and the difficulty of spectral assignment. Recently, individual Na⁺ hydrates, hydronium-water layers and alkali ion-water chains were successfully visualized by noncontact atomic force microscopy (AFM) with a carbon monoxide (CO)-terminated tip. This development opens up the possibility of probing interfacial ion-water interactions with atomic precision. In this work, the researchers investigated the extended network formed by different alkali metal cations and water molecules on a charged Au(111) surface in real space, which constitutes an ideal model system to understand the atomic structure at electrolyte/electrode interface