Electrochemical Characterization of Water–Oil Interfaces in the Presence of Nanoparticles for Enhanced Oil Recovery

Enhanced oil recovery (EOR) critically depends on understanding and controlling electrostatic phenomena at the oil–water–rock interface, where interfacial charge governs key recovery mechanisms in porous media. To date, no practically applicable methodology has been reported for the direct determination of interfacial charge, particularly at liquid–liquid interfaces where nanoscale interactions dictate macroscopic behavior. Instead, interfacial electrical properties are commonly inferred indirectly through molecular dynamics (MD) simulations or experimental estimation of the zeta potential, which represents the electric potential at the slipping plane of the electrical double layer (EDL). This work introduces an electrochemical voltammetry framework based on cyclic voltammetry (CV) to characterize the interfacial charge and capacitance at the oil/brine interface. This advanced approach enables quantitative evaluation of the interfacial charge and provides deeper physical insight into the electrostatic interactions governing interfacial phenomena. Core–shell Fe3O4@C nanoparticles (NPs), in the presence of brine ions and asphaltenes in the oil phase, are employed as a model colloidal system to investigate interfacial properties through electrochemical mechanisms. Distinct interfacial capacitance responses are identified, demonstrating strong sensitivity to the ionic strength and NP-induced interfacial restructuring. Variations in asphaltene-like surface-active species further modify the charge-capacitance behavior, highlighting the coupling between molecular adsorption and the electrochemical response. Systematic measurements reveal that NP concentration, asphaltene content, and brine composition significantly shift interfacial tension (IFT) and electrocapillary curves, providing a quantitative pathway to correlate macroscopic interfacial forces with nanoscale charge distribution. Overall, this study demonstrates a unified analytical methodology that connects voltammetric signals, interfacial capacitance, and physicochemical interfacial properties, enabling the precise characterization and rational design of functional nanoparticles, ionic environments, and surface-active systems for enhanced oil recovery applications.