Electrode
Definition and meaning of Electrode in chemistry.
An electrode is an electrical conductor that connects to an electrolyte inside an electrochemical cell. It is usually made of metal, graphite, or another material that conducts electrons well. Electrodes carry electric current into or out of a solution through oxidation or reduction reactions.
In more detail
Chemists classify electrodes by which reaction happens at their surface. Oxidation occurs at the anode, releasing electrons into the external circuit. Reduction occurs at the cathode, consuming electrons from the circuit.
Electrodes can be active or inert. Active electrodes, like zinc or copper, take part in the chemical reaction and get consumed or built up over time. Inert electrodes, like platinum or graphite, simply provide a surface for electron transfer without reacting themselves.
Electrodes are central to two types of electrochemical cells. Galvanic cells, also called voltaic cells, use spontaneous reactions at their electrodes to generate electrical energy. Electrolytic cells do the opposite, using an external power source to force a nonspontaneous reaction to occur at their electrodes.
The overall voltage of an electrochemical cell, called the cell potential, depends on the difference in tendency of the two electrode reactions to occur. Standard reduction potentials are measured in volts against a reference hydrogen electrode. These values let chemists predict which electrode will act as the cathode and calculate a cell's overall voltage before building it.
Electrode surfaces are sometimes coated or specially shaped to increase surface area, which improves reaction efficiency in devices like fuel cells.
Key facts
| Field | Physical Chemistry |
|---|---|
| Anode | Site of oxidation (electron loss) |
| Cathode | Site of reduction (electron gain) |
| Common inert materials | Platinum, graphite |
| Common active materials | Zinc, copper |
| Used in | Galvanic (voltaic) cells and electrolytic cells |
In a Daniell cell, a zinc metal electrode acts as the anode, where Zn is oxidized to Zn2+ and 2 electrons. A copper metal electrode acts as the cathode, where Cu2+ gains those 2 electrons and is reduced to solid Cu. A salt bridge connects the two half-cells to complete the circuit.
Frequently asked questions
What is the difference between an electrode and an electrolyte?
The electrode is the solid conductor where electron transfer occurs. The electrolyte is the ionic solution or molten compound that carries current between electrodes through ion movement rather than electron flow.
Is the anode always the negative electrode?
No. In a galvanic (voltaic) cell the anode is negative, but in an electrolytic cell the anode connects to the positive terminal of the external power source. In both cases, oxidation always occurs at the anode.
What is the difference between an active and an inert electrode?
An active electrode participates in the redox reaction and is chemically changed, like a zinc electrode being consumed as it oxidizes. An inert electrode, like platinum, only conducts electrons without reacting itself.