Anode and Cathode in Electrolytic vs. Galvanic Cells

The biggest point of confusion for students is that the polarity (`+` or `-`) of the anode and cathode seems to switch depending on the type of cell. However, the definition based on the chemical reaction is always the same.

The Universal Rule: AN OX (Anode = Oxidation) and RED CAT (Reduction = Cathode) is true for ALL cells.

1. Galvanic Cell (or Voltaic Cell)

A galvanic cell produces electricity from a spontaneous chemical reaction.

• Example: A discharging battery (like an AA battery) or a car battery.
• Anode: Oxidation occurs here, releasing electrons into the circuit. This surplus of electrons gives the anode a Negative (`-`) charge.
• Cathode: Reduction occurs here, consuming electrons from the circuit. This deficit of electrons gives the cathode a Positive (`+`) charge.

2. Electrolytic Cell

An electrolytic cell uses an external power source to drive a non-spontaneous chemical reaction.

• Example: Recharging a battery, electrolysis of water, or electroplating.
• Anode: Oxidation still occurs here. However, the external power source pulls electrons away from this electrode, forcing the non-spontaneous oxidation to happen. This "pulling" action means the anode is connected to the external source's positive terminal, so the anode is Positive (`+`).
• Cathode: Reduction still occurs here. The external power source pushes electrons onto this electrode, forcing the non-spontaneous reduction to happen. This "pushing" of electrons means the cathode is connected to the external source's negative terminal, so the cathode is Negative (`-`).

Feature Galvanic Cell (Battery) Electrolytic Cell (Recharging)