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I know how the voltaic cell normally works, producing current. It is not what I'm asking about. I know that normally, the Zinc electrode slowly dissolves (it is anode, $\ce{Zn -2e^- -> Zn^{2+}}$), passing electrodes to the Copper electrode at which $ H^+ $ ions from the acid electrolyte get reduced to $ H_2 $ (it is cathode, $\ce{2H^+ +2e^- -> H_2}$) Thereby creating electric current.

Now my question is, what if we passed current from an external voltage source to that cell? Not in the same direction of current, like an in series battery would be connected, but in the opposite direction?

By doing this, I hope to block the flow of electrons from the Zinc electrode (and to get it to stop dissolving?) Then reduce some cations, like $ H^+ $ or even $ Zn^{2+} $ after I run out of $ H^+ $, which is more easily reduced?

And oxidize the anion of the acid of the electrolyte on the copper electrode?

Are any of my ideas correct?

I am sorry if this is a bad question, I am a beginner. Please don't hate me, it's my first time posting here and I tried googling.

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    $\begingroup$ No question is a bad question as long as there is some effort. Ignore negative down votes too. This is habitual. I think you are not searching the right terms. Search charging and discharging a battery for an overall concept. Also search null point potentiometry. It does quite the same thing which you are thinking. If you apply an external potential to a voltaic cell in the opposite direction, the cell reaction will stop and depending on the external applied voltage, that voltaic cell can become an electrolytic cell. $\endgroup$
    – ACR
    Commented Mar 12, 2023 at 20:25
  • $\begingroup$ @AChem Thanks. Do I understand correctly though, that the voltaic cell cannot be recharged, as the first cations to be reduced would be H+, so during the "recharging" attempt they would all form hydrogen gas? And that there will be no acid as electrolyte left then. $\endgroup$
    – Petr L.
    Commented Mar 12, 2023 at 20:46
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    $\begingroup$ Can you add the chemical equations of the cell you are thinking about? What are the half cells made of? The voltaic cell can be recharged if it is rechargeable. $\endgroup$
    – ACR
    Commented Mar 12, 2023 at 20:56
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    $\begingroup$ Petr L, No that is not a classical cell. A standard cell is one where the metal is in contact with its ions in solution. $\endgroup$
    – ACR
    Commented Mar 13, 2023 at 15:32
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    $\begingroup$ Petr L, Yes, I have read about Voltaic pile for ages. What I was trying to tell you is that Voltaic pile is not amenable to Nernst equation treatment. Also, please write the half cell reactions you are thinking about in your original question. $\endgroup$
    – ACR
    Commented Mar 13, 2023 at 18:51

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$\ce{Zn - Cu}$ is not much used these days.The common Leclanché $\ce{Zn - C}$ "flashlight" cell is not rechargeable, for the reason you give.

However, alkaline cell chemistry, such as $\ce{Zn - Mn}$, has less outgassing of $\ce{H2}$ during reverse current, and there are rechargeable $\ce{Zn - Mn}$ cells. To further reduce $\ce{H2}$ production, or to recycle it back to water,

  • "The cathode has a catalyst to recombine any hydrogen that forms..."
  • "Zinc oxide is added to the cathode mix to,... on charge,... form oxygen."

So, at useful charging voltage, both recharging (i.e., plating zinc metal back) and evolution of hydrogen take place. However, one branch of that reaction can be made to be favored over the other.

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  • $\begingroup$ Very interesting, thanks! How does zinc oxide being added help? EDIT: I see that it can be dissolved in bases, but why does it take priority over reducing H+? $\endgroup$
    – Petr L.
    Commented Mar 13, 2023 at 7:47

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