I think we need more information.

What is your electrolyte solution, alkaline or acidic?

What about impurities in your electrolyte? Are gases involved in your work?

Can you show an example CV to learn more about your "instability"?

Kind regards

Peter

Thank you for your answer!

I am using 0.5 M sulfuric acid from prepared from Merck suprapur sulfuric acid and 18.2 mega Ohm water. This should be fine. I also took great care when preparing the electrolyte and carefully cleaned the flask beforehand.

Regarding gases: i am purging the solution with Ar from the house supply for 40 minutes before operation.

Concerning the CV: unfortunately i do not have a CV at hand right now, but what happens is the following: The sharp feature of the Pt(111) butterfly peak diminished after 5 minutes and is gone completely by minute 30. The broad feature of the butterfly peak also gets smaller.

Thank you for your help!

Without seeing the CV we can only guess. Pt or support dissolution - potential range?  Any other peaks occuring instead?

Kind regards

Peter

I am working with a single crystal - there is no support.

The potential range is 0.05 V to  0.6 V.

Also, no other peaks occur

thank you and warm regards

Gregor

Dear Gregor Zwaschka,

an EIS measurement (if available) will illuminate your research.

Hi Gregor,

how do you clean your glassware and cell? Glass and Teflon shoud be just fine for your experiments. If you are not using it already, you can try cleaning everything with RCA1 cleaning (5 parts of ultrapure water, 1 part ~30% NH3, 1 part 30% H2O2) for 30 min at 70-80 °C, prior to your experiments.

In your case it might also be a mass transport related problem, do you work with a rotating disc electrode or do you stir your electrolyte?

It is a long shot, but you might have Cl- diffusion into your electrolyte from your RE, if you are using a Ag/AgCl. You could consider switching to a SO4 filled RE.

Regards

Ozlem

I forgot to mention that RCA1 is quite aggressive for most polymers and organic contaminations, take appropriate precautions...

There is no doubt glass is the cleanest surface than any other material.

Piranha solution is the best cleaning solution for both glassware and Teflon, specially when working with single crystal. It is very strong oxidizing solution and the residual Piranha solution can be removed easy, just by heating your cell in ultrapure water

Thank you for the answers, they are highly appreciated.

For the cleaning procedure:

-immersing of the glass-ware in basic permanganate solution for 24 h

-thorough rinsing with pure water

-immersing in a solution of sulfuric acid + hydrogen peroxide

-thorough rinsing with water

-boiling in ultrapure water for 10 min

-thorough rinsing with ultrapure water

I am using a Hg2SO4 reference electrode, even though it contains the same anions i dont think it is very clean. Could this cause problems? I am switching to a home-made reference electrode that only uses Pt and H2.

Dear Oslem Ozcan:

could you please elaborate on the issue of transport limitation? In fact, i do not stir the solution, neither am i working with a RDE.

A big thank you to all of you

Gregor

Dear Artur Braun,

could you please elaborate on the stability of Pt? Do you mean that the electrode is inherently instably, i.e., that if you start with a perfectly clean cell, electrolyte, etc., that the CV will still get worse with time? If so, do you have any numbers regarding the time scale of this degradation in mind?

Thank you very much

Gregor

Hi Gregor,

since I don't know, how your CV curves look like, I can only guess at this point, According to your description, your oxidation/reduction peaks dissapear assymetrically. You've said some of them dissapear completely, and others get smaller. What I've meant was, especially if you suspect impurities, you may have some irreversible reactions on your electrode, so that the reverse reaction is not possible at all. This might be caused by the inhibition of electron transfer, as well as depletion of reactants. What sweep rates are you using, did you test different sweep rates? Does it happen at all sweep rates?

We used to clean gold coated AFM cantilevers with Piranha (sulfuric acid/H2O2) solution and had trouble with getting rid of S-containing contaminations. Even with boiling in water, we've observed S in XPS, trying RCA1 could help.

Good luck

Ozlem

Dear Gregor Zwaschka,

show us some of your CV graphs. Also, note, please, which are the problems (specify them on the graphs).

Glass, especially pyrex can be made cleaner than teflon by all the known methods. 

Please excuse the delay, i have been very busy the last days. Here are some Pt(111) CVs from an analog writer (preliminary experiments). The CVs were recorded using the Hg2SO4 reference electrode, 0.5 M H2SO4, 50 mV/s

1) almost ideal Pt(111) CV in the hanging meniscus mode

2) & 3) teflon wrapped electrode completely immersed in the solution, 2) shows a gradual decrease in the intensity of the butterfly peaks until it vanishes almost completely. 3) the red curve shows the very beginning of the experiment, then the potential was held in the UPD region (around the blue circle) for 10 min, then the green curves were recorded, recording time for the green CVs also was 10 min.

I do not understand what do you mean by Teflon wrapped electrode?

Firstly. for single crystal work, very clean condition is required and you have to anneal your crystal prior to your experiment.

So, how will you wrap it after that with Teflon, you will contaminate your crystal.

Secondly, are you sure that your electrolyte can not go beneath the Teflon and the Pt surface especially you wait for 10 minutes. Because if the electrolyte go between Teflon and Pt, you will not have a pure Pt (111) behavior as the sides of your electrode are polycrystalline.

It is better to show up your electrode

as Alaa A. El-Shafe , note :  it is better to show up, please, your cell (and electrodes).

Dear Gregor, please check this video 

http://web.ua.es/es/eqsup/monocristales/preparacion-de-una-celula-electroquimica.html

Pt(111) CV can be stable for hours, maybe the spike around 0.45 V can dimish from 100uA/cm2 to 80uA/cm2 after two hours. Glassware is ok, just boil more times.

Dear Ricardo Martinez-Hincapie,

thank you for your response, it is really useful and highly appreciated. The videos are highly informative and surpisingly well to understand for someone who does not speak spanish.

What i could not figure out: Should i repeat the whole process including immersing in permanganate, rinsing with H2O2 and H2SO4, etc. for 3-6 times, or only the boiling in ultra-pure water? And if i got it right one boiling process should last for 2-3 hours?

One more question: do you maybe know a vendor for ultra-clean Teflon band? For spectroscopic measuremeants i need to wrap everything except the single crystal facet im interested in in Teflon. Or is there an efficient way to clean teflon band? Maybe i could proceed just as with the glas ware.

Thank you again, also: Prof. Feliu really is the master of single crystal electrochemistry.

Best

Gregor

Dear Gregor, you only need boiling in ultra-pure water for 3-6 times. One boiling is not enough. I use some Teflon pieces for IR and I clean in the same way that glassware.

Ricardo