Galvanic cells convert chemical energy to electrical energy spontaneously. Anode is negative (site of oxidation), cathode is positive (site of reduction). Electrons flow from anode to cathode through the external circuit. Salt bridge completes the circuit and maintains electrical neutrality. $E_{cell}$ > 0 and $delta_G$ < 0. Electrolytic cells use external electrical energy to drive non-spontaneous reactions. The polarity is reversed: anode is positive (connected to positive terminal of battery), cathode is negative. $E_{cell}$ < 0 and $delta_G$ > 0 for the cell reaction. The minimum voltage needed equals |$E_{cell}$| of the reverse reaction, plus overpotential. In both cell types, oxidation occurs at the anode and reduction at the cathode — this NEVER changes.