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.