Galvanic (electrochemical) cell
A spontaneous redox reaction does work. Chemical energy → electrical energy. The more reactive metal (Zn) is oxidised at the negative anode; less reactive Cu²⁺ is reduced at the positive cathode. E°cell > 0.
Electrolytic cell
An external power supply drives a non-spontaneous reaction. Electrical energy → chemical energy. The battery pulls electrons from the anode (now +) and pushes them onto the cathode (now −). Polarity is set by the battery, not the chemistry.
Ion migration
In both cells, cations always migrate toward the cathode and anions toward the anode — the electrolyte carries the charge. The signs of the electrodes flip between cell types, but the rule "cation → cathode" never does.
Selective discharge
In aqueous electrolytes, what is discharged depends on position in the electrochemical series, concentration, and the electrode material. Compare molten NaCl (Na, Cl₂) with brine (H₂, Cl₂) to see why water can win at the cathode.