The classic voltaic cell has a $\ce{Zn}$ anode and $\ce{Cu}$ cathode. The reduction half reaction occurring at the cathode combines aqueous copper ions and electrons supplied by the anode to form solid $\ce{Cu}$. So what is the purpose of the $\ce{Cu}$ cathode? $\ce{Cu}$ is produced anyways from the electrons supplied by the anode. Why can't we have instead of the $\ce{Cu}$ cathode, simply the wire connecting to the anode which will supply electrons to fuel the reduction half reaction?


You could certain have a zinc-copper cell in which copper was not the cathode material. Graphite or silver or whatever could be the electrode material instead. But once you close the circuit:

  1. Current flows
  2. Cu is deposited as a metal solid on the electrode surface, whatever it is made out of.
  3. Copper metal is, as it always is, conductive.
  4. As a result of steps 2 and 3, there is now a copper metal cathode instead of a cathode made of another material.

So even if you start without a copper cathode you wind up with one.


You could have a cathode made from something other than $\ce{Cu}$, however, this reaction will only produce $\ce{Cu{(s)}}$ as a result if the metal used for the cathode is a weaker reducing agent than $\ce{Zn}$, otherwise the $\ce{Zn}$ electrode would become plated in $\ce{Zn{(s)}}$.

Using a $\ce{Mg}$ electrode in the $\ce{Cu^{2+}}$ solution, for example, would result in the $\ce{Zn}$ electrode to become plated with $\ce{Zn{(s)}}$.


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