Hello,

which kind of RE are you using? Normally KCl is used as electrolyte if it is based on the Ag/AgCl or calomel system. Using KOH would need a so-called double junction RE. For very small currents the cell should be placed in a Faraday cage and grounded to the measurement instrument. Another source could be the electrical contact of the RDE (dirt on the contact areas).  

I would start troubleshooting with the RDE. It depends on the type of rotator you are using, specifically the type of electrical contact used. For Pine rotators the contacts are brushes. It is recommended to clean the brush chamber every two weeks of continuous use. If the rotator is very old, the brushes may be worn out and need to be replaced. Noise due to dirty or worn down contacts are not an issue if you are using a mercury-based electrical contact. Gas evolution is also a contributor of noise in RDE experiments, so depending on your catalyst's efficiency toward the 4 electron ORR mechanism, you may be actually evolving O2 gas by decomposition of peroxide intermediate at higher rotation speeds and more positive potentials (or on the other hand, if the noise is noticeable more pronounced at more negative applied potentials, then your catalyst may be facilitating H2 evolution, even in alkaline conditions, and generating hydrogen bubbles). Bubble formation and release causes periodic high intensity fluctuations in the current which can appear to be noise in the CV and usually the associated peak-to-peak noise level increases with increasing current.

If you come to find that the issue isn't related to the RDE, then I would check your reference electrode, your lead cables/alligator clips, and grounding. The recommended reference electrode for ORR in 0.1 M KOH is Hg/HgO.

Are periodic noises? If they are, try to connect the rotator in another electrical line. Maybe you have coupling signals and this produce the interference.

I agree with the above suggestions and add another one: do the noise depend on RDE rate. If so, something is wrong with it and other causes can be ruled out.

agree with all above..shaft wobble, poor contacts, nearby electrical interference from rf sources, poor grounding, ..... of course some depend on the current scale (gain) while other sources of noise are mechanical and will show up at all ranges...

Thank you so much for all valueble answers. From Donald Robinson, I would like to ask about brush more detial. Where it is located in the Pine rotator. When I measure empty measurement under N2 flow at  rpm, there is a lot of noise in CV. However, with rotation, the noise is considerably reduced. My RE is Hg/HgO in 0.1M KOH.

Our experiment showed that hidrogen evolution was the main cause of noise...Nitrogen flow reduce it

Oyunbileg,

The carbon/silver brush contacts do not look like regular brushes with bristles. They are marked red on the outside and are where you attach your working electrode cable. Attached is the Pine rotator manual, which goes over the routine maintenance and common troubleshooting issues.

So you have higher noise without rotation? Then the noise may be caused by something else, perhaps the experimental conditions. When you say "under N2 flow" you don't mean that you are bubbling N2 while acquiring the CV, right? I usually bubble N2 for 10 minutes to drive out O2, then keep the gas gently flowing above the solution during measurement. You want to avoid gas bubbles as much as possible, whether evolved or introduced, to minimize environmental noise.

Evolved gas bubbles have interfered with my experiments too, Antonio. Sometimes nothing I do can control it and I just accept the noise and explain it in the discussion.

Thank you so much for your comment and file.

Of course you should stop N2 bubbling during measurements!

First, record cyclic voltammetry in KOH only to see if you have noise. If yes, it come obviously from your Reference Electrode. What do you use as RE?

It can be a problem of the experimental setup on your computer.