Cathode
The cathode is the electrode at which reduction occurs in an electrochemical cell, with species gaining electrons from the electrode. In a galvanic (voltaic) cell, the cathode is the positive terminal because reduction of cations (gain of electrons) takes place there and it has a higher electrode potential; in an electrolytic cell, the cathode is connected to the negative terminal of the power supply. The mnemonic "Red Cat" (Reduction at Cathode) helps students remember this consistent rule across all types of electrochemical cells.
Cathode Behaviour in Different Electrochemical Cells
| Cell Type | Cathode Polarity | Process at Cathode | Example Reaction | Example |
|---|---|---|---|---|
| Galvanic cell | Positive (+) | Reduction (spontaneous) | Cu²⁺ + 2e⁻ → Cu | Daniel cell Cu cathode |
| Electrolytic cell | Negative (−) | Reduction (driven) | 2H⁺ + 2e⁻ → H₂ | Water electrolysis |
| Electroplating | Negative (−) | Metal deposition | Ag⁺ + e⁻ → Ag | Silver plating |
| Fuel cell | Positive (+) | O₂ reduction | O₂ + 4H⁺ + 4e⁻ → 2H₂O | Hydrogen fuel cell |
| Electrolytic refining | Negative (−) | Pure metal deposit | Cu²⁺ + 2e⁻ → Cu | Pure Cu cathode |
Interactive Tools
PhET Electrochemistry Simulation
Observe reduction reactions at the cathode in an interactive electrochemical cell
Open ToolKhan Academy – Anodes and Cathodes
Comprehensive lesson on cathode processes, polarity, and comparison with anodes
Open ToolBrilliant – Electrolytic Cells and Cathodes
Practice problems and theory on cathode reduction reactions in various cell types
Open Tool
Wikimedia Commons, CC BY-SA
Related Terms
Anode
The anode is the electrode at which oxidation occurs in an electrochemical cell, with species losing electrons to the electrode and the electrons flowing into the external circuit. In a galvanic (voltaic) cell, the anode is the negative terminal because it loses electrons and has a lower electrode potential; in an electrolytic cell, the anode is connected to the positive terminal of the external power supply. The key memory rule is that the anode always hosts oxidation, regardless of the type of cell, and can be remembered by the mnemonic "An Ox" (Anode = Oxidation).
Galvanic Cell
A galvanic cell (also called a voltaic cell) is an electrochemical device that converts chemical energy into electrical energy through spontaneous redox reactions occurring at two electrodes separated by an electrolyte. The oxidation half-reaction occurs at the anode (negative terminal) and the reduction half-reaction occurs at the cathode (positive terminal), with electrons flowing through an external circuit. Galvanic cells are the basis of all batteries and are fundamental to understanding energy storage and conversion in chemistry.
Electrolysis
Electrolysis is a process in which an electric current is passed through an electrolyte (an ionic compound in solution or molten state) to drive non-spontaneous chemical reactions, decomposing the electrolyte into its constituent elements or ions at the electrodes. At the cathode, cations are reduced by gaining electrons, while at the anode, anions are oxidised by losing electrons. Electrolysis has wide industrial applications including the production of chlorine and sodium hydroxide (chlor-alkali process), extraction of aluminium (Hall–Héroult process), electroplating, and water splitting to produce hydrogen fuel.
Coined by Michael Faraday in 1834 from Greek "kathodos" meaning "the way down" (kata = down, hodos = way or path), referring to the direction of conventional current flow descending into the electrolyte at the cathode, by the convention used at the time.