Description
Ion-specific effects at electrode interfaces fundamentally govern interfacial microscopic structure, charge distribution, and reaction kinetics, thereby controlling device performance in electrocatalysis, sensing, and energy conversion applications. Here, we employ electrically tunable, substrate-free monolayer graphene as a model platform to systematically probe the electric double layer (EDL) structure of alkali halide electrolytes at carbon electrode interfaces, using phase-sensitive sum-frequency vibrational spectroscopy (SFVS) complemented by electrochemical measurements. By quantitatively decomposing the total interfacial sum-frequency response into contributions from the diffuse layer, Stern layer , and graphene, we directly determine the density of desolvated halide anions within the SL and reconstruct the molecular-scale structure of the interfacial ionic layers. Remarkably, specifically adsorbed halide anions at the outermost graphene surface exhibit pronounced charge transfer with the electrode, with the magnitude of transfer increasing with ionic size.
