I synthesized Mn-Co mixed oxide with conductive polymer PEDOT through anodic electrodeposition method on glassy carbon electrodes. The way I am doing the experiments to prove that the catalyst is active towards oxygen reduction and oxygen evolution is as follows:
1) Purging Ar for 20 mins in 0.1 M KOH, afterwards I am conducting cyclic voltammetry at -0.7 to 0.1 Vs Hg/HgO
2) Purging O2 for 10 mins and doing CV at the same potential window.
3) Starting LSV with RDE at 100,400,900,1600,2500 rpms (-0.7 to 0.2 V) while I am purging oxygen into solution.
4) LSV test at 1600 rpm (0.1-0.7 V) to test OER activity
Overall, I never get plateau shaped LSV curves at the end and the results are very inconsistent in terms of kinetic current and shape of the curve. Sometimes I get a huge reduction peak at more positive potential. Any idea?
Could your potential range not be the suitable?
I think that you are applying low anodic potentials. Maybe you should do a cyclic voltammetry with a huge range to detect the potential range where OER occurs.
I also agree that the potential range is not the appropriate. Theoretically you should see the oxygen evolution at minimum of 0.5V vs Hg/HgO at pH=13 but first you need to spurge with Ar or N2. The real starting point will be higher than 0.5V.
Later for study the oxygen reduction, I recommend you to go from 1V at least to 0V vs Hg/HgO. If you go from 0.1V to 0.7 V you are oxidizing. Take care if PEDOT and the glassy carbon can evolve CO2.
Thank You Jordi and Pau. Yes, actually you guys are right I need to go to higher potential to see OER, and I usually see OER peak if I increase the potential window to more positive. But my problem is the cathodic reaction which is ORR in LSV experiment. If you are familiar with the shape of the curves at different rotation speeds, they are "S" shaped with a plateau. My curves does not have a plateau, they look like a half "S". Furthermore, is some cases I get lower kinetic current at 2500 compare to 1600.
Dear Ellie Davari
that is due the oxygen storage of the mixed oxides, That is the capacity of the manganese oxide, which is used in some other kind of batteries as well.
You just should pay attention to the onset potential, that means the catalytic activity.
You should furthermore work the the RHE electrode instead of the Hg/HgO.
Hans
I think you either did not reach the diffusion limited current region, as you do not have a plateau yet, or your loading did not homogeneously cover the Substrate with a thin layer film, which is required for any RDE. I suggest to go a bit more negative in potential. and check your catalyst loading if it is on GC. Moreover, i prefer well saturation of Oxygen in solution and then just purging over the solution surface.
Dear Hatem, thank you for your response. Do you have any idea why I dont get diffusion limited current ? Is it because of not good coverage or the low intrinsic activity of catalysts? Other question is what did you mean by well saturation of oxygen, is there any other method other than purging gas inside the solution?
Dear Ellie, Diffusion limited current is not related to your activity, but the current in the mixed kinetic-diffusion region (ca. 0.6-0.9 V RHE)is of interest. I think it is more related to your surface and particle distribution on it. I don't know how well covered it your surface, and if you have contribution of GC or not. For saturation, you can just purge over the solution during the exp.
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