In an electric double layer capacitor(EDLC) (or any situation with a Helmholtz double layer) what prevents the ions from being reduced or oxidized like the ions in an electrochemical cell?

If it is because the potential is not high enough, what energy barrier is preventing the reaction?

In the negative ion case, is it that even though the ion has a net negative charge and as a whole is attracted the the positive electrode the electron feels a stronger attraction the the nucleus than the the electrode?

Is this what determines the maximum voltage of a supercapacitor?

How does all of this relate to the inner and outer layers?

Sorry for so many questions in one post but I think they are all related and I hope that they provide context for my confusion.

  • $\begingroup$ Ok. I have searched and read pretty deeply. EDLC and Redox electrochemistry are covered for sure but I did not find any discussion of why they are not conflicting ways of describing what happens at the liquid solid interface of a conductor and an ionic solution. I could certainly have missed it. Maybe I didn't search the correct terms. If you find such a discussion please let me know I would be happy to be wrong and have missed an explanation. Clearly I'm no expert hence the need to ask the question. $\endgroup$ Jan 22, 2022 at 18:48

1 Answer 1


In hopes of helping others that have the same question, I think a have a partial answer. From https://www.sciencedirect.com/science/article/pii/B9780124095472111497

"Traditionally, electrochemical double-layer theory has been concerned with the so-called ideally polarizable interfaces, at which by definition no electrochemical reaction takes place and hence no direct current passes through the interface."

I still have not found a definition of "ideally polarizable interfaces" that helps me but I think the point is that any voltage applied if below the redox potential.

I hope this helps. I will keep working on it.

  • $\begingroup$ More definitions an ideally polarizable electrode has no Faradic current. "Faradaic current is the current generated by the reduction or oxidation of some chemical substance at an electrode. en.m.wikipedia.org/wiki/Faradaic_current $\endgroup$ Jan 22, 2022 at 20:35

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