In a voltaic (galvanic) cell, the cathode is the electrode where reduction occurs.
This means:
- Electrons from the external circuit flow into the cathode.
- Positive ions from the solution gain these electrons at the cathode.
- As a result, a chemical species in the solution is reduced (its oxidation state decreases).
In simple terms, the cathode receives electrons and is the site where the chemical reaction gains electrons.
For example, in a zinc-copper cell, copper ions in the solution gain electrons at the copper cathode and form solid copper.
So, the cathode is always the place of reduction in a voltaic cell.