Surface‐Enhanced Raman Detection of Interfacial Water Enabled by Electrolyte‐Specific Reconstruction of Hydrogen‐Bond Network Defects in the Electric Double Layer

Interfacial water governs charge transfer, adsorption, proton transport, and catalytic selectivity at aqueous solid–liquid interfaces, yet its O−H Raman response remains difficult to resolve by surface‐enhanced Raman scattering (SERS). This study correlates the emergence of interfacial‐water SERS signatures with electrolyte‐specific reconstruction of the local hydrogen‐bond environment within the electric double layer. In situ electrochemical SERS, constrained O−H band deconvolution, quantum‐chemical cluster calculations, and molecular dynamics simulations are combined to compare roughened Ag electrodes in 1.0 M KCl and NaCl. The spectra reveal pronounced electrolyte‐ and potential‐dependent redistribution of the interfacial O−H stretching response, accompanied by distinct ion‐hydration, hydrogen‐bond, and orientational structures in the simulations. Chloride‐associated interfacial species provide a plausible chemical‐enhancement contribution, whereas the more compact Na + hydration environment correlates with a larger retained high‐wavenumber O−H contribution. The combined results support a mechanistic picture in which electrolyte‐induced hydration‐network reconstruction may modify intermolecular vibrational coupling and energy redistribution, thereby contributing to the SERS detectability of interfacial water.