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I'm new to electrochemistry and I was wondering two things, sorry if these two problems are trivial but I just can't find anything close to this in the literature.

First, the following reaction is irreversible, right? an intermediate Q is formed:
$B + e^{-} \rightarrow Q$

and another reaction follows where it is converted to a different product X:

$Q \rightarrow X$.

Then I'm supposed to sketch a cyclic voltammogram (CV) of this process, but I was taught that for irreversible processes a CV is not useful.

I looked pretty much all day for a similar reaction and the closest I could find is in "A Practical Beginner’s Guide to Cyclic Voltammetry" where the following reactions are presented:

$\text{Ox} + e^{-} \rightleftharpoons \text{Red}$

$\text{Red} \rightarrow Z$

These are defined as EC coupled reaction: reversible electron transfer Er following by an irreversible homogeneous chemical reaction Ci.

The ones I am given are not the same, I think. But I have no idea how to sketch a CV for that process. Am I interpreting the given reactions wrongly?

enter image description here

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  • $\begingroup$ Look at en.wikipedia.org/wiki/Cyclic_voltammetry. In the cathodic scan, the scan voltage goes from more positive to less positive w.r.t. the reference potential. Then you get a reduction of B to Q. Then Q irreversibly goes to X, which is not electroactive. So the reverse scan shows no oxidation peak current because Q is gone and X is not electroactive, i.e., it cannot be significantly oxidized in the CV situation. $\endgroup$ – Ed V Jul 19 at 19:18
  • $\begingroup$ Thank you for your reaction. What you describe seems like an irreversible process, which should look something like this, I think (see figure in question, don't know how to add it here). $\endgroup$ – Paperreader Jul 19 at 19:26
  • $\begingroup$ Yes, that is correct. $\endgroup$ – Ed V Jul 19 at 19:29
  • $\begingroup$ Alright. I'm glad I asked this, otherwise I would have assumed that the first reaction was irreversible. So it is an entirely irreversible reaction then. Thanks! $\endgroup$ – Paperreader Jul 19 at 19:35
  • $\begingroup$ Yes, I found a similar explanation in this source (see below). At slower scan rates the cyclic voltammogram would look similar to what I posted in my question. Thanks for the clarification! <chem.libretexts.org/Bookshelves/Analytical_Chemistry/…> $\endgroup$ – Paperreader Jul 19 at 19:47

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