An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte or a vacuum). The word was coined by the scientist Michael Faraday from the Greek words elektron (meaning amber, from which the word electricity is derived) and hodos, a way.
Anode and cathode in electrochemical cells
An electrode in an electrochemical cell is referred to as either an anode or a cathode (words that were also coined by Faraday). The anode is now defined as the electrode at which electrons leave the cell and oxidation occurs, and the cathode as the electrode at which electrons enter the cell and reduction occurs. Each electrode may become either the anode or the cathode depending on the direction of current through the cell. A bipolar electrode is an electrode that functions as the anode of one cell and the cathode of another cell.
A primary cell is a special type of electrochemical cell in which the reaction cannot be reversed, and the identities of the anode and cathode are therefore fixed. The anode is always the negative electrode. The cell can be discharged but not recharged. Unlike secondary cells, primary cells are used instantaneously.
A secondary cell, for example a rechargeable battery, is one in which the chemical reactions are reversible. When the cell is being charged, the anode becomes the positive (+) and the cathode the negative (−) electrode. This is also the case in an electrolytic cell. When the cell is being discharged, it behaves like a primary cell, with the anode as the negative and the cathode as the positive electrode.
Other anodes and cathodes
In a vacuum tube or a semiconductor having polarity (diodes, electrolytic capacitors) the anode is the positive (+) electrode and the cathode the negative (−). The electrons enter the device through the cathode and exit the device through the anode. Many devices have other electrodes to control operation, e.g., base, gate, control grid.
In a three-electrode cell, a counter electrode, also called an auxiliary electrode, is used only to make a connection to the electrolyte so that a current can be applied to the working electrode. The counter electrode is usually made of an inert material, such as a noble metal or graphite, to keep it from dissolving.
In arc welding an electrode is used to conduct current through a workpiece to fuse two pieces together. Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shielded metal arc welding, or non-consumable, such as in gas tungsten arc welding. For a direct current system the weld rod or stick may be a cathode for a filling type weld or an anode for other welding processes. For an alternating current arc welder the welding electrode would not be considered an anode or cathode.
Alternating current electrodes
For electrical systems which use alternating current the electrodes are the connections from the circuitry to the object to be acted upon by the electric current but are not designated anode or cathode since the direction of flow of the electrons changes periodically, usually many times per second.
Uses of electrodes
Electric currents are run through nonmetal objects to alter them in numerous ways and to measure conductivity for numerous purposes. Examples include:
- Electrodes for medical purposes, such as EEG, ECG, ECT, defibrillator
- Electrodes for electrophysiology techniques in biomedical research
- Electrodes for execution by the electric chair
- Electrodes for electroplating
- Electrodes for arc welding
- Electrodes for cathodic protection
- Electrodes for grounding
- Electrodes for chemical analysis using electrochemical methods
- Inert electrodes for electrolysis (made of platinum)
- Membrane electrode assembly
- Working electrode
- Reference electrode
- Redox Reaction
- Cathodic protection
- Galvanic cell
- Anion vs. Cation
- Electron versus hole
- Electron microscope
- Tafel equation
- Hot cathode
- Cold cathode
- ^ Faraday, Michael (1834). "On Electrical Decomposition". Philosophical Transactions of the Royal Society. Archived from the original on 2010-01-17. http://www.webcitation.org/5mq8a85S3. Retrieved 2010-01-17. ( (in which Faraday coins the words electrode, anode, cathode, anion, cation, electrolyte, electrolyze)
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électrode — [ elɛktrɔd ] n. f. • 1836; angl. electrode (1834); de electric et ode 1 ♦ Électr. Conducteur par lequel le courant arrive ou sort dans un électrolyte, un tube à gaz raréfié et, en général, un milieu où il doit être utilisé. Électrode positive. ⇒… … Encyclopédie Universelle
Electrode — Électrode La pile de Volta : le zinc à l anode est consommé en libérant des électrons qui alimentent le circuit électrique. Une électrode est un conducteur métallique, ou ionique (ex. verre) relié à une demi pile ou faisant partie d une demi … Wikipédia en Français
Electrode — E*lec trode ([ e]*l[e^]k tr[=o]d), n. [Electro + Gr. odo s way, path: cf. F. [ e]lectrode.] (Elec.) a conducting object by which electricity is conveyed into or from a solution or other non metallic conducting medium; esp., the ends of the wires… … The Collaborative International Dictionary of English
Electrode — сингл солиста группы ТОЛ, The Obolon Bastardz, Гаплык. Трек лист: Електрод 4:26 Порушити закон 5:18 Торба (вместе с «Гаплик») 3:53 Чорний дощ (вместе с Василий Переверзев (Prozorow) (ТОЛ)) 5:56 Оззі, будь ласка не вбивай 3:06 Вихід? 4:49 Біти… … Википедия
Electrode — Electrode. См. Электрод. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) … Словарь металлургических терминов
electrode — 1834, coined by English physicist and chemist Michael Faraday (1791 1867) from ELECTRO (Cf. electro ) + Gk. hodos way (see CEDE (Cf. cede)) on same pattern as ANODE (Cf. anode), CATHODE (Cf. cathode) … Etymology dictionary
electrode — ► NOUN ▪ a conductor through which electricity enters or leaves something. ORIGIN from ELECTRIC(Cf. ↑electrically) + Greek hodos way , on the pattern of anode and cathode … English terms dictionary
electrode — [ē lek′trōd΄, ilek′trōd΄] n. [ ELECTR(O) + ODE1] any terminal that conducts an electric current into or away from various conducting substances in a circuit, as the anode or cathode in a battery or the carbons in an arc lamp, or that emits,… … English World dictionary
electrode —  In a spark plug one electrode (the center electrode) is the center rod passing through the insulator. The side electrode is a rod welded to the shell of the spark plug. The distance between them is the spark gap.  In welding it is the… … Dictionary of automotive terms
Électrode — La pile de Volta : le zinc à l anode est consommé en libérant des électrons qui alimentent le circuit électrique. Une électrode est un conducteur électronique, ou ionique (ex. verre) relié à une demi pile ou faisant partie d une demi pile,… … Wikipédia en Français