Dear Dr. Manisha Pandey ,

in order to have a complete answer, I suggest you to have a look at the following, interesting document:

- Open Circuit Potential: an incredibly versatile measurement

By GerardMacias - December 1, 2023

Available at: https://maciassensors.com/open-circuit-potential/

My best regards, Pierluigi Traverso.

Good questions! Here are some points about open circuit potential (OCP) measurements and what they indicate:

• When the OCP stabilizes or reaches a steady-state value, it means the sample surface is likely reaching an equilibrium state where the anodic and cathodic reactions are proceeding at equal rates.
• It does not necessarily mean a protective passive film has formed. Passivity should be confirmed through other techniques like electrochemical impedance spectroscopy or direct surface analysis.
• A stable OCP also does not automatically mean corrosion is occurring. You need to assess whether the value lies in the active, passive, or immune regions for that particular metal-environment combination.

Some reasons why your Tafel Ecorr values may not match well with stabilized OCP:

• The Tafel scan starts perturbing the system as soon as the potential deviates from the OCP during the sweep. So it does not directly assess the natural free corrosion condition.
• Surface condition changes - Tafel and OCP tests may be done after different surface preparation and exposure periods.
• Differences in oxygen availability, temperature, or electrolyte composition/stirring between tests can shift Ecorr relative to OCP.
• There may be noise or inaccuracies in either measurement leading to errors.

I would ensure environmental test conditions are controlled and consistent between OCP and electrochemical tests. Also verify proper operation of the reference electrode as it sets the potential baseline.