[CopperSmurf]

Hi everyone! So in electrochemistry, usually platinum is cleaned in some kind of strong acid to eventually get a typical shape by cyclic voltammetry. So, I tried it out and got a really weird set of bumps around -0.05 V, see the attached jpeg pic. It's platinum with a Ag/AgCl reference in 1M sulfuric acid. What the *beep* are those weird bumps?

*edit* I tried repeated cycling and concenrated acid, it doesn't go away.

[Jack Bauer]

Lots of unanswered electrochemistry on here - I may end up wasting my day.

Anyway, what is your electrode surface?  Is it a bulk Pt electrode e.g., a disk?

1 M sulfuric acid is stronger than normally used.  I would suggest 0.5 but regardless, the bumps at negative potentials look like hydrogen adsorption, which you would expect (see chapter 13 I think of bard electrochemistry text book).  However, the problem is the crossover just before them, this should not be happening.  What was your scan rate?

Either way, potential cycling is fine for cleaning your electrode but if possible polishing on with a alumina powder first is best.  Then, perform c.a. 50 cycles in your current potential range at 500 mVs-1.  After this record you CV and it should be perfect!  btw, looks like you did not remove oxygen before you started that measurement, if you did then you have some resistance in your setup.

Hope this helps.

Quick edit - your positive potential limit of 1.2 is a bit high.  If you have gone to the trouble of fabricating particular crystal facets they wont last long at 1.2 vs. Ag/AgCl. 

[CopperSmurf]

Anyway, what is your electrode surface?  Is it a bulk Pt electrode e.g., a disk?
It's a bulk Pt electrode (wire).

1 M sulfuric acid is stronger than normally used.  I would suggest 0.5 but regardless, the bumps at negative potentials look like hydrogen adsorption, which you would expect. 
Ya, but hydrogen adsorption is usually to the left of that ugly bumpy crossover.

What was your scan rate?
Scan rate was 0.1 V/s. Weird thing is that it only shows up at that scan rate and slower rates. At higher scan rates, that bumpy crossover isn't there.

ya, my setup does have some resistance and didn't bother to remove oxygen since I was doing a quick run to see if those bumps were still there. Have not thought of polishing, will maybe give that a try when I get the polishing kit. Pt is expensive :S

Quick edit - your positive potential limit of 1.2 is a bit high.  If you have gone to the trouble of fabricating particular crystal facets they wont last long at 1.2 vs. Ag/AgCl. 
Currently not looking at certain Pt crystal facets.

Thanks for replying!