Dear All,
I am trying to calculate the tafel slope of a potentiodynamic polarization curve. However I have some doubts about how to select the right points or regions. As selecting different regions will significantly alter the tafel slopes and corrosion rate. Can anyone guide me through this? I have enclosed the two images of my polarization curve.
Dear Junaid Ul Hasnain
The Tafel slope is only anodic, cathodic reaction is under diffusion control (probably oxygen reduction) followed by hydrogen evolution, so there is no cathodic Tafel slope which is valid only for activation controlled reaction. In two graphs you probably obtain the same value for anodic slope, but for the cathodic extremely high, higher than >200 mV/dec dependent of selected region.
the best way is using the software of your potentiostat, as dr. grgur said only anodic slop is important.
You have to adjust the cathodic slope in accordance to the anodic one, in a way that they cross the Ecorr line
Please look at the following below links which may help you in your analysis:
https://www.gamry.com/assets/Uploads/EchemAnalystSoftwareManual.pdf
https://pineresearch.com/shop/kb/software/software-help-and-support/using-aftermath/generate-tafel-aftermath/
https://www.c3-analysentechnik.de/wp-content/uploads/2015/12/5601_3-Gamry-Software-DC105.pdf
Thanks
Two cases should consider to determining the anodic and cathodic tafel solp graphically:
- The electrolyte solution is alkaline and the cathodic reaction rate is solely controlled by mass transport then linearizes the anodic branch first.
- The electrolyte solution is acidic or near neutral and the cathodic reaction rate is solely controlled by mass transport and activated charge transfer then linearize the cathodic branch first.
Now, after linearization of the first branch, get the intersect point with the corrosion potential line and then linearize the second branch starting from the obtained point of intersect.
Finally the tafel slop of both anodic and cathodic parts ready to determine graphically.
Best regards
Dear Prof. Branimir N. Grgur , thank you for your answer. Indeed the cathodic tafel slope in my curve is very large compared to the anodic slope. However I need certain values from both slopes for polarization resistance experiment. I also don't know yet what are the limits for selecting the linear regions on the tafel diagram in order to calculate these slopes. If you could clarify them for me.
https://www.gamry.com/assets/Uploads/EchemAnalystSoftwareManual.pdf
Aimal Khan, Please have a look; it might be relevant in your situation.
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