Dear Mohsen Feyzi,

I don't know your system, but what I can tell you is that an unstable OCP could originate from many factors, and one of them is that the chemistry at the surface of your WE is slightly changing during the OCP measurement: for example, you might have some chemical reactions going on at the surface.

It might be interesting to run first 3 cycles of Cyclic Voltammetry between +1V and -1V and then check the OCP and see if it is more stable. Also after doing this you can change the electrolyte and check the OCP again. Maybe you need to "clean" electrochemically the surface of your electrode.

Question: did you check your OCP after the LSV run?

Also why the time of OCP is set for 2 hours? maybe 1 to 5 minutes is enough.

Cheers,

Francesco

Hi Francesco,

Thanks for your answer and attention.

With anytime of OCP (5 mins or 2 hrs), the voltage does not stablise. This time was selected based on some research in literature.

Regarding the solution, we have also tested with salty water; however, the problem is still there.

We have not yet run the LSV. Does the polarisation need this?

Regards,

Mohsen.

... the problem is still there, dear Mohsen Feyzi,

since various aging activities of your medical (polycrystalline[1], and multi-material electrode) Ti6Al4V in the PBS solution, follow, at least, two major (but contractual) mechanisms:

1) add-on material(s) by complex surface corrosion and

2) subtraction of material(s) by surface film dissolution in the PBS solution.

1. Precision Hard Turning of Ti6Al4V Using Polycrystalline Diamond Inserts... https://pubmed.ncbi.nlm.nih.gov/33322699/

@ Ioannis Samaras

Thanks for your answer. We have this behavior for other metals as well; such as steel and aluminium.

Dear Mohsen Feyzi ,

what are the specs (mainly it's purity[1]) of your samples of the Aluminum (alloy[2] ?) ?

Also, what are the specs (technical coding#) of your samples of the steel[3] ?

A hint: Try, initially, another pure sample (Pt, Au, etc.) if you would like to test, mainly, your methods or cells.

1. https://www.researchgate.net/post/Why_aluminum_wire_does_not_dissolve_in_HCl

2. Aluminum (alloys):

2a. The Aluminum Association Alloy and Temper System https://www.aluminum.org/sites/default/files/AEC%20presentation%20160224.pdf

2b. Understanding the Aluminum Alloy Designation System https://www.esabna.com/us/en/education/blog/understanding-the-aluminum-alloy-designation-system.cfm

3. Stainless Steel (Technical coding):

3a. Stainless Steel: Tables of Technical Properties https://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Tables_TechnicalProperties_EN.pdf

3b. AISI-SAE CLASSIFICATIONS OF STEELS https://weldinghandbook.com/wp-content/uploads/2017/02/steel-classification-codes.pdf

3c. AISI Steel Code Tables https://www.steel.org/steel-technology/steel-production/outside-processors/aisi-steel-code-tables/ https://www.steel.org/wp-content/uploads/2021/03/STLCDPID_10-30-19.xlsx

@ Ioannis Samaras

Thanks for your answer.

I will check these points.

Regards,

Mohsen.

Dear Mohsen,

If I was you, I would run the LSV three times and then see if the OCP gets more stable. Did you try this?