# Why does the cathode have to be made out Cu in a Zn-Cu voltaic cell?

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 $$\ce{Zn{(s)}}$$.