electrode

An electrode is a conductor through which electric current enters or leaves the non-metallic part of an electrical circuit, typically in an electrochemical cell or device. In electrochemistry, electrodes enable electron transfer between an external circuit and chemical species in an electrolyte. The electrode surface participates in redox reactions, and the potential at the interface depends on the redox couple and the state of the electrode–electrolyte interface. A charged layer forms at the interface, known as the electrical double layer, which contributes to capacitance and reaction kinetics.

Electrodes are commonly categorized as anodes and cathodes according to their role in a cell. In galvanic (discharging) cells the anode is the source of electrons and is oxidized; in electrolytic (driven) cells the anode is the positive terminal where oxidation occurs if current direction reverses. Laboratory measurements often use a three-electrode setup with a working electrode, a reference electrode, and a counter electrode to control the potential and separate current paths.

Materials vary with application. Inert electrodes such as graphite, carbon, platinum, and gold are used when they participate minimally in chemistry; reactive metals can participate in the redox process. Reference electrodes, including silver/silver chloride or saturated calomel, provide stable potentials for measurement. Electrode choice depends on conductivity, chemical stability, and compatibility with the electrolyte.

Applications include energy storage (batteries and supercapacitors), electroplating and electrolysis, corrosion testing, sensors, and medical devices for electrical recording or stimulation. Safety and handling focus on preventing contamination, avoiding damage to the interface, and ensuring proper insulation and connections.