Monitoring transient changes in the structure of water at a polarised liquid-liquid interface using electrocapillary curves

[Display omitted] •An ITIES is non-equilibrated upon formation.•The interfacial energy at the ITIES shifts to lower values with time.•Such shifts hamper precise measurement of the differential capacitance.•Real time interfacial energy measurements are possible during potential steps.•Such measurements detect transient interfacial electrolyte structure changes. The interface between two immiscible electrolyte solutions (ITIES) is a close approximation of an ideally polarisable interface, being non-equilibrated upon formation. Despite this, the formalism of equilibrium thermodynamics, e.g., electrocapillary equations, are universally applied to interpret electrochemical processes at the ITIES. This communication shows that interfacial energy measurements in real time during step potential experiments are a useful tool to detect transient changes in the structure of the electrolyte solutions at the ITIES, in particular in the presence of chaotropes or kosmotropes in the aqueous electrolyte. Molecular dynamics computer simulations substantiate our findings, quantifying the perturbation of the atomic-scale structure, dynamics and energetics of the interface in the presence of a kosmotrope.