Electrodes

An electrode is a conductor through which electric current enters or leaves an electrically conductive medium such as an electrolyte or semiconductor. In electrochemistry, electrodes are immersed in electrolyte solutions and participate in redox reactions at their surfaces. They serve as interfaces between the electrical circuit and the chemical species involved.

Anodes and cathodes describe where oxidation or reduction occurs, but their role depends on the cell type. In galvanic cells the anode is the source of electrons (oxidation) and the cathode consumes electrons (reduction). In electrolytic cells an external power source drives oxidation at the anode and reduction at the cathode. Electrodes may be active, participating in the chemical reaction, or inert, serving mainly as conductors (for example zinc in a cell vs platinum or graphite).

Common electrode materials include carbon, platinum, gold, and silver/silver chloride, as well as various metals and conductive polymers. Surfaces can be treated or coated to improve conductivity, selectivity, or biocompatibility. The electrode–electrolyte interface forms a double layer and enables Faradaic or non-Faradaic processes; its properties influence impedance, response time, and sensitivity.

Applications span energy storage and conversion, including batteries and supercapacitors, and electrolysis processes such as water splitting and chlor-alkali production. Electrodes are also central to sensing and medicine, enabling electrochemical sensors, electrocardiography (ECG), electroencephalography (EEG), and neural interfaces. Reference electrodes, such as Ag/AgCl or the standard hydrogen electrode, provide stable potentials for measurement.

Emerging directions include microelectrodes, flexible and printed electrodes, and nanoengineered surfaces designed to improve interfacing with biological tissue and analytical performance.