Electrochemical overpotentials (V3+/V4+ redox)

[tinska.h]

Hey,

Does anyone know a good source for overpotentials on carbon / graphite electrodes? Especially looking data for V4+ + 2H+ + e- <-> V3+ + H2O (+0.34V vs. SHE) overpotential. Or are there any ways to estimate the overpotentials?

Thanks

 

[TeethWhitener]

I'm going to take a stab at this, but I don't know how much help I can be with your specific question. So it looks like the reaction you're looking for is reduction of the vanadyl cation to V³⁺.
$$VO^{2+} +2H^+ + e^- \rightarrow V^{3+} + H_2O$$
This is the reaction that I found with a potential of +0.34V vs. SHE. This means maybe you're looking for information about cross-contamination in vanadium redox flow batteries? A quick lit search yields a few papers that may be of some interest:
http://pubs.acs.org/doi/abs/10.1021/la00009a054
http://ecst.ecsdl.org/content/35/32/11.short
This last one has kinetics info about vanadyl reduction, but nothing specifically on overpotentials.
http://onlinelibrary.wiley.com/doi/...ionid=9952D8759BBB8B5B3D01A5E8277E1316.f04t01
This one is as close as I've gotten: it's a system looking specifically at the reduction of VO(acac) to V(acac) in an acidic acetonitrile environment over glassy carbon electrodes. You might want to follow the references from this one.
Sorry I couldn't be of more help. Best of luck.

 

[tinska.h]

Hey, Thanks for your effort!

Yeah it seems that there's very limited data regarding VO2+ -> V3+. I saw few articles where the graphs indicated much larger overpotential for the VO2+ and V3+ redox pair compared to V3+/V2+ and V5+/V4+.

 

[TeethWhitener]

Hey, Thanks for your effort!

Yeah it seems that there's very limited data regarding VO2+ -> V3+. I saw few articles where the graphs indicated much larger overpotential for the VO2+ and V3+ redox pair compared to V3+/V2+ and V5+/V4+.

This makes sense. You'd want to use half-reactions that are well-separated in potential if they're going to have a common redox ion.