Electrode

An **electrode** is an electrical conducted 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. [|[] 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. It is usually made up of a primary and a secondary cell. The primary cell identifies the anode and cathode and then they are fixed. The secondary cell also identifies the anode and cathode but will allow them to change.

Also, 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.

Primary 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.

Secondary cell
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.

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.