Diagram of a zinc anode in a galvaniccell. Note how electrons move out ofthe cell, and the conventional currentmoves into it in the opposite direction.From Wikipedia, the free encyclopediaAn anode is an electrode through which positive electric chargeflows into a polarized electrical device. The flow of charge is anelectric current. A common mnemonic is ACID for Anode CurrentInto Device; the key notion is a positive current flows into thedevice; positive charges are entering the device through the anode.There is a complication because a current is often moving electrons,and the charge on an electron is negative. Positive charge flowinginto the anode is the same as (negative) electrons flowing out out ofthe anode. Consequently, the direction of electric current is oppositeto the direction of electron flow: electrons flow out of the anode tothe outside circuit.A widespread misconception is that anode polarity is always positive(+). This is often incorrectly inferred from the correct fact that in allelectrochemical devices, negatively charged anions move towards theanode. Actually, by the above universal definition of electric currentdirection, anode polarity depends on the device type and, sometimes,even on its operating mode. Consequently, as can be seen from thefollowing examples, the anode is positive in a device that consumespower, and the anode is negative in a device that provides power:In a discharging battery or galvanic cell (diagram at right), the anode is the negative terminal becauseit is where the current flows into "the device" (i.e. the battery cell). This inward current is carriedexternally by electrons moving outwards, negative charge moving one way constituting positivecurrent flowing the other way.In a recharging battery, or an electrolytic cell, the anode is the positive terminal, which receivescurrent from an external generator. The current through a recharging battery is opposite to thedirection of current during discharge; in other words, the electrode which was the cathode duringbattery discharge becomes the anode while the battery is recharging.In a diode, the anode is the positive terminal at the tail of the arrow symbol (base of the triangle),where current flows into the device. Note electrode naming for diodes is always based on the directionof the forward current (that of the arrow, in which the current flows "most easily"), even for typessuch as Zener diodes or solar cells where the current of interest is the reverse current.In a cathode ray tube, the anode is the positive terminal where electrons flow out of the device, i.e.,where positive electric current flows in.An electrode through which current flows the other way (out of the device) is termed a cathode.1 Etymology2 Flow of electrons3 Electrolytic anode4 Battery or galvanic cell anode5 Vacuum tube anode6 Diode anode7 Sacrificial anode8 Related antonymAnode - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Anode1 di 5 22/04/2014 10.449 See also10 References11 External linksThe word was coined in 1834 from the Greek (anodos), 'ascent', by William Whewell, who had beenconsulted[1] by Michael Faraday over some new names needed to complete a paper on the recentlydiscovered process of electrolysis. In that paper Faraday explained that when an electrolytic cell is orientedso that electric current traverses the "decomposing body" (electrolyte) in a direction "from East to West, or,which will strengthen this help to the memory, that in which the sun appears to move", the anode is wherethe current enters the electrolyte, on the East side: "ano upwards, odos a way ; the way which the sun rises"(,[2] reprinted in [3]).The use of 'East' to mean the 'in' direction (actually 'in' 'East' 'sunrise' 'up') may appear contrived.Previously, as related in the first reference cited above, Faraday had used the more straightforward term"eisode" (the doorway where the current enters). His motivation for changing it to something meaning 'theEast electrode' (other candidates had been "eastode", "oriode" and "anatolode") was to make it immune to apossible later change in the direction convention for current, whose exact nature was not known at the time.The reference he used to this effect was the Earth's magnetic field direction, which at that time was believedto be invariant. He fundamentally defined his arbitrary orientation for the cell as being that in which theinternal current would run parallel to and in the same direction as a hypothetical magnetizing current looparound the local line of latitude which would induce a magnetic dipole field oriented like the Earth's. Thismade the internal current East to West as previously mentioned, but in the event of a later conventionchange it would have become West to East, so that the East electrode would not have been the 'way in' anymore. Therefore "eisode" would have become inappropriate, whereas "anode" meaning 'East electrode'would have remained correct with respect to the unchanged direction of the actual phenomenon underlyingthe current, then unknown but, he thought, unambiguously defined by the magnetic reference. In retrospectthe name change was unfortunate, not only because the Greek roots alone do not reveal the anode's functionany more, but more importantly because, as we now know, the Earth's magnetic field direction on which the"anode" term is based is subject to reversals whereas the current direction convention on which the "eisode"term was based has no reason to change in the future.Since the later discovery of the electron, an easier to remember, and more durably correct technicallyalthough historically false, etymology has been suggested: anode, from the Greek anodos, 'way up', 'the way(up) out of the cell (or other device) for electrons'.The flow of electrons is always from anode to cathode outside of the cell or device, regardless of the cell ordevice type and operating mode, with the exception of diodes, where electrode naming always assumescurrent in the forward direction (that of the arrow symbol), i.e., electrons flow in the opposite direction, evenwhen the diode reverse-conducts either by accident (breakdown of a normal diode) or by design (breakdownof a Zener diode, photo-current of a photodiode or solar cell).In electrochemistry, the anode is where oxidation occurs and is the positive polarity contact in an electrolyticcell. At the anode, anions (negative ions) are forced by the electrical potential to react chemically and giveoff electrons (oxidation) which then flow up and into the driving circuit. Mnemonics: LEO Red Cat (Loss ofAnode - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Anode2 di 5 22/04/2014 10.44Galvanic cellCutaway diagram of a triode vacuumtube, showing the plate (anode)Electrons is Oxidation, Reduction occurs at the Cathode), or AnOx Red Cat (Anode Oxidation, ReductionCathode), or OIL RIG (Oxidation is Loss, Reduction is Gain of electrons), or Roman Catholic and Orthodox(Reduction Cathode, anode Oxidation), or LEO the lion says GER (Losing electrons is Oxidation,Gaining electrons is Reduction).This process is widely used in metals refining. For example, in copper refining, copper anodes, anintermediate product from the furnaces, are electrolysed in an appropriate solution (such as sulfuric acid) toyield high purity (99.99%) cathodes. Copper cathodes produced using this method are also described aselectrolytic copper.In a battery or galvanic cell, the anode is the negative electrode fromwhich electrons flow out towards the external part of the circuit.Internally the positively charged cations are flowing away from theanode (even though it is negative and therefore would be expected toattract them, this is due to electrode potential relative to theelectrolyte solution being different for the anode and cathodemetal/electrolyte systems); but, external to the cell in the circuit,electrons are being pushed out through the negative contact and thusthrough the circuit by the voltage potential as would be expected.Note: in a galvanic cell, contrary to what occurs in an electrolyticcell, no anions flow to the anode, the internal current being entirely accounted for by the cations flowingaway from it (cf drawing).In the United States, many battery manufacturers regard the positive electrode as the anode, particularly intheir technical literature. Though technically incorrect, it does resolve the problem of which electrode is theanode in a secondary (or rechargeable) cell. Using the traditional definition, the anode switches endsbetween charge and discharge cycles.In electronic vacuum devices such as a cathode ray tube, the anode isthe positively charged electron collector. In a tube, the anode is acharged positive plate that collects the electrons emitted by thecathode through electric attraction. It also accelerates the flow ofthese electrons.In a semiconductor diode, the anode is the P-doped layer whichinitially supplies holes to the junction. In the junction region, theholes supplied by the anode combine with electrons supplied fromthe N-doped region, creating a depleted zone. As the P-doped layersupplies holes to the depleted region, negative dopant ions are leftbehind in the P-doped layer ('P' for positive charge-carrier ions). Thiscreates a base negative charge on the anode. When a positive voltageis applied to anode of the diode from the circuit, more holes are ableto be transferred to the depleted region, and this causes the diode tobecome conductive, allowing current to flow through the circuit. Theterms anode and cathode should not be applied to a Zener diode,since it allows flow in either direction, depending on the polarity of the applied potential (i.e. voltage).Anode - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Anode3 di 5 22/04/2014 10.44Sacrificial anodes mounted "on the fly"for corrosion protection of a metalstructureIn cathodic protection, a metal anode that is more reactive to thecorrosive environment of the system to be protected is electricallylinked to the protected system, and partially corrodes or dissolves,which protects the metal of the system it is connected to. As anexample, an iron or steel ship's hull may be protected by a zincsacrificial anode, which will dissolve into the seawater and preventthe hull from being corroded. Sacrificial anodes are particularlyneeded for systems where a static charge is generated by the actionof flowing liquids, such as pipelines and watercraft.In 1824 to reduce the impact of this destructive electrolytic action onships hulls, their fastenings and underwater equipment, the scientist-engineer Sir Humphry Davy, developed the first and still most widelyused marine electrolysis protection system. Davy installed sacrificial anodes made from a more electricallyreactive (less noble) metal attached to the vessel hull and electrically connected to form a cathodicprotection circuit.A less obvious example of this type of protection is the process of galvanising iron. This process coats ironstructures (such as fencing) with a coating of zinc metal. As long as the zinc remains intact, the iron isprotected from the effects of corrosion. Inevitably, the zinc coating becomes breached, either by cracking orphysical damage. Once this occurs, corrosive elements act as an electrolyte and the zinc/iron combination aselectrodes. The resultant current ensures that the zinc coating is sacrificed but that the base iron does notcorrode. Such a coating can protect an iron structure for a few decades, but once the protecting coating isconsumed, the iron rapidly corrodes.If, conversely, tin is used to coat steel, when a breach of the coating occurs it actually accelerates oxidationof the iron.At least one anode is found in tank-type water heaters. The anode should be removed and checked after 5years (sooner if there is a sodium based water softner inline), and replaced if 15 cm (6 inches) or more ofbare wire is showing. This will greatly extend the life of the tank.The opposite of an anode is a cathode. When the current through the device is reversed, the electrodesswitch functions, so anode becomes cathode, while cathode becomes anode, as long as the reversed currentis applied, with the exception of diodes where electrode naming is always based on the forward currentdirection.Anodising (a method of enhancing the surfaceproperties of aluminium)BatteryDiodeCathodic protectionElectron tubeElectrolysisRedox (oxidation-reduction)Primary cellGalvanic anodeAnode - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Anode4 di 5 22/04/2014 10.44^ Ross, S (1961). "Faraday Consults the Scholars: The Origins of the Terms of Electrochemistry". Notes andRecords of the Royal Society of London (19381996) 16 (2): 187220. doi:10.1098/rsnr.1961.0038(http://dx.doi.org/10.1098%2Frsnr.1961.0038).1.^ Faraday, Michael (January 1834). "Experimental Researches in Electricity. Seventh Series"(http://www.gutenberg.org/ebooks/14986). Philosophical Transactions of the Royal Society 124 (1): 77.doi:10.1098/rstl.1834.0008 (http://dx.doi.org/10.1098%2Frstl.1834.0008). (in which Faraday introduces thewords electrode, anode, cathode, anion, cation, electrolyte, electrolyze)2.^ Faraday, Michael (1849). Experimental Researches in Electricity (http://www.gutenberg.org/ebooks/14986) 1. 3.The Cathode Ray Tube site (http://www.crtsite.com)How to define anode and cathode (http://www.av8n.com/physics/anode-cathode.htm)Valence Technologies Inc. battery education page (http://www.valence.com/technology/battery_overview.html)Cathodic Protection Technical Library (http://www.cathodicprotectionpapers.com)Retrieved from "http://en.wikipedia.org/w/index.php?title=Anode&oldid=604784759"Categories:ElectrodesThis page was last modified on 18 April 2014 at 19:53.Text is available under the Creative Commons Attribution-ShareAlike License; additional terms mayapply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia is a registeredtrademark of the Wikimedia Foundation, Inc., a non-profit organization.Anode - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Anode5 di 5 22/04/2014 10.44