Electrochemical corrosion measurements in low-conductivity bio-oils: Decoupling interfacial film memory from bulk electrolyte aging

• Electrochemical measurement sequence gives consistent corrosion ranking across electrolytes of varying viscosity. • Three-configuration aging matrix separates interfacial memory from bulk aging effects. • Ohmic drop corrected linear polarization resistance (R p (LPR)) conversed with R p of electrochemical impedance spectroscopy (R p (EIS)). • Four-electrode configuration outperforms three-electrode configuration in viscous, low-conductivity media. Electrochemical corrosion measurements in viscous, low-conductivity organic media are limited by high cell impedance and parasitic artefacts. This work showcases a robust electrochemical protocol validated in a model bio-oil (MBO, 135 cP) and a more viscous pristine fast pyrolysis bio-oil (P-FPO, 7780 cP) to obtain reliable corrosion kinetic parameters. Established best practices, including open circuit potential (OCP) stabilization, low-amplitude perturbations, and an electrochemical impedance spectroscopy (EIS) acquired within a charge-transfer-focused frequency window were implemented using a four-electrode cell. Experiments were performed in MBO under three aging systems: Same Solution-Same Electrode (SSSE), Same Solution-Different Electrode (SSDE), and Different Solution-Different Electrode (DSDE). EIS analysis with a physically motivated equivalent circuit resolved the solution resistance (R s ), charge transfer resistance (R ct ), and EIS-derived polarization resistance (R p (EIS)), thereby decoupling the contributions of interfacial film growth and bulk-solution aging to the measured resistances. Uncompensated linear polarization resistance (LPR) slopes initially overestimated R p (LPR) due to the contribution of R s ; after ohmic drop (iR) correction using EIS-derived R s , R p (LPR) converged with R p (EIS), enabling rapid yet quantitative corrosion screening. Cross-comparison between MBO and P-FPO systems confirms that a properly wired four-electrode configuration is essential for quantitative corrosion measurements in highly resistive, highly viscous, polymer-rich organic media particularly when solution resistance is uncertain.