Anode and Cathode in Electrochemical Cells

Full Notes

Introduction: What Is an Electrochemical Cell?

Electrochemical cells use redox (reduction–oxidation) reactions to either produce electricity or use electricity to drive chemical changes.

They are essential for understanding how chemical energy is converted into electrical energy through the movement of electrons and ions.

There are two main types of electrochemical cells:

• Voltaic (Galvanic) cells which generate electricity from a spontaneous redox reaction.
• Electrolytic cells which use electricity to force a non-spontaneous redox reaction to occur.

Where Does Redox Happen?

All electrochemical cells contain two solid electrodes placed into a liquid (electrolyte).

• The anode is the electrode where Oxidation always happens.
• The cathode is the electrode where Reduction always happens.

(Remember oxidation = loss of electrons, reduction = gain of electrons).

The sign (positive/negative) of each electrode depends on the type of cell.

Voltaic (Galvanic) Cells

Voltaic, also called galvanic, cells produce electrical energy from a redox reaction that happens without any external energy needed (spontaneous).

Electrons flow through an external wire from the anode to the cathode.

• The Anode (where oxidation occurs) is negatively charged.
• The Cathode (where reduction occurs) is positively charged.

Example: Zinc–copper cell

Anode (Zn): Zn → Zn²⁺ + 2e⁻

Cathode (Cu): Cu²⁺ + 2e⁻ → Cu

Electrolytic Cells

Electrolytic cells use electrical energy to drive a chemical change.

An external power source forces electrons through the cell.

• The Anode (where oxidation occurs) is positively charged.
• The Cathode (where reduction occurs) is negatively charged.

Example: Electrolysis of molten NaCl

At the anode (positive): 2Cl⁻ → Cl₂(g) + 2e⁻

At the cathode (negative): Na⁺ + e⁻ → Na(s)

Matt’s exam tip

Always remember: oxidation happens at the anode, and reduction happens at the cathode. Don't memorise based on positive or negative charges — those switch between voltaic and electrolytic cells. Focus on the reaction type instead: it's consistent every time.

Summary Table

Summary

• Oxidation occurs at the anode and reduction at the cathode
• Voltaic cells generate electricity spontaneously
• Electrolytic cells use electricity to drive non-spontaneous reactions
• Electrode signs depend on whether the cell is voltaic or electrolytic