As you know in corrosion experiments, one of the theoretical investigations of the accuracy of the experimental tafel curve is to plot all of the probable anodic and cathodic reactions curve in E vs. Log i. For example, in an acidic solution which is saturated by CO2 gas, cathodic reactions are as following:
1- Reduction of H+ ions in acidic solution
2- Reduction of H2CO3
3-Reduction of H2O
4-Reduction of bicarbonate ions
And Anodic reactions include the steel dissolution in the saturated CO2 test solution.
So, How would you plot these theoretical reactions along with your obtained polarization curve plotted by potentiostat? Is there any software that you use to plot them or you get the equation and then plot the curve by yourself?
Please see the attached picture and then participate in this technical disscussion in order to open details from electrochemical points of view and discuss about them
Dear Askar Soltani ,
The calculations of partial cathodic and/or anodic curves in such complex systems require a lot of unknown parameters for some exact case. For example, reversible potentials for given reactions, exchange current density of the reaction at the given electrode, transfer coefficient or Tafel slope, even worst is for mixed activation-diffusion reactions, among enumerated parameters diffusion coefficient in a given solution. So, in my opinion, this will be a tricky business. For some less complex systems, for example, corrosion of Fe, Zn in acidic or neutral solutions could be possible.
Dear Professor Branimir N. Grgur ,
Thanks for your contribution. As you said based on Tafel or Butler-Volmer equation for plotting E-Logi in potentiodynamic polarizations we need to have required kinetic parameters including exchange current density of the cathodic species and the metal in the electrolyte, Tafel slopes and overpotential. In this case by having the mentioned kinetic parameters, we also need to apply Butler-Volmer equation for a numeric system for example in Excell by considering voltage steps (Overpotential steps) for example steps of 1 mV for (E-Ecorr) and calculate the associated current density and then by having a set of points in the coordination of (E-Ecorr, current density) for X and Y axes we can plot E versus i abd then compare to the net anodic and cathodic curves which observe in potentiodynamic polarization plot by the potentiostat.
Ohio university has released a free add-in (Named Freecorp) for Excell which plot cathodic and anodic reactions potentiodynamic plots in CO2 saturated environments and i think they follow the Butler-Volmer equation in their software and it was very interesting for me to find out the following questions in this regard:
1 - How they consider the amount of exchange current density of cathodic species ?
2 - How they determine limiting current density for cathodic species ?
3 - Is there Butler-Volmer equation used in plotting theoretical cathodic and anodic polarization plots or another theoretical equation has been applied?
If you and your students are interested to continue this topic, please contribute or share this topic
I appreciate it in advance
Best regards,
Askar Soltani
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