Get charged up: Nonlinear optical voltammetry for quantifying the thermodynamics and electrostatics of metal cations at aqueous/oxide interfaces

► The Eisenthal χ(3) method quantifies adsorption electrostatics, thermodynamics, and kinetics. ► The method is label-free and applicable to any optically transparent system. ► The sensitivity for aqueous/fused silica interfaces exceeds 0.01% of a monolayer. ► Mg, Ca, Sr, and Ba surface coverages follow size-dependent trends. ► New directions include interfacial potential models for uncharged systems.