An electrode is a 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, whence the word electricity is derived) and hodos, a way [1].
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2 Other uses of anode and cathode 3 Types of electrode 4 References |
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 defined as the electrode at which oxidation occurs, and the cathode is defined as the electrode at which reduction occurs. Each electrode may become either the anode or the cathode depending on the type of reaction occurring in the 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. It can be discharged but not recharged. The anode is always the negative (-) electrode and the cathode always the positive (+).
A secondary cell, for example a rechargeable battery, is one in which the reaction is reversible. When the cell is being charged, the anode becomes the positive (+) electrode and the cathode the negative (-). This is also the case in an electrolytic cell. When the cell is being discharged, it behaves like a primary or voltaic cell, with the anode as the negative electrode and the cathode as the positive.
In a vacuum tube or a semiconductor having polarity (diodes, electrolytic capacitorss) the anode is the positive (+) electrode and the cathode the negative (-).
Anode vs. cathode in electrochemical cells
Other uses of anode and cathode
Types of electrode
References
Michael Faraday, "On Electrical Decomposition", Philosophical Transactions of the Royal Society, 1834 (in which Faraday coins the words electrode, anode, cathode, anion, cation, electrolyte, electrolyze).