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| [[Image:Cyclovoltammogram.jpg|thumb|300px|right|Typical cyclic voltammogram where <math>i_{pc}</math> and <math>i_{pa}</math> show the peak cathodic and anodic current respectively for a reversible reaction.]]
| | This is a preview for the new '''MathML rendering mode''' (with SVG fallback), which is availble in production for registered users. |
| '''Cyclic voltammetry''' or CV is a type of [[voltammetry|potentiodynamic]] [[electrochemistry|electrochemical]] measurement. In a cyclic voltammetry experiment the working electrode potential is ramped linearly versus time like [[linear sweep voltammetry]]. Cyclic voltammetry takes the experiment a step further than linear sweep voltammetry which ends when it reaches a set potential. When cyclic voltammetry reaches a set potential, the working electrode's potential ramp is inverted. This inversion can happen multiple times during a single experiment. The current at the working electrode is plotted versus the applied voltage to give the cyclic voltammogram trace. Cyclic voltammetry is generally used to study the electrochemical properties of an [[analyte]] in solution.<ref>{{Cite book | |
| | edition = 2
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| | publisher = Wiley
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| | isbn = 0-471-04372-9
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| | last = Bard
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| | first = Allen J.
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| | coauthors = Larry R. Faulkner
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| | title = Electrochemical Methods: Fundamentals and Applications
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| | date = 2000-12-18
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| }}</ref><ref name="Nicholson">{{Cite journal
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| | doi = 10.1021/ac60210a007
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| | volume = 36
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| | issue = 4
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| | pages = 706–723
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| | last = Nicholson
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| | first = R. S.
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| | coauthors = Irving. Shain
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| | title = Theory of Stationary Electrode Polarography. Single Scan and Cyclic Methods Applied to Reversible, Irreversible, and Kinetic Systems.
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| | journal = Analytical Chemistry
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| | accessdate = 2009-04-17
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| | date = 1964-04-01
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| }}</ref><ref>{{Cite journal
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| | doi = 10.1002/anie.198408313
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| | volume = 23
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| | issue = 11
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| | pages = 831–847
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| | last = Heinze
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| | first = Jurgen
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| | title = Cyclic Voltammetry-"Electrochemical Spectroscopy". New Analytical Methods (25)
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| | journal = Angewandte Chemie International Edition in English
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| | accessdate = 2009-04-17
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| | year = 1984
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| }}</ref>
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| == Experimental method ==
| | If you would like use the '''MathML''' rendering mode, you need a wikipedia user account that can be registered here [[https://en.wikipedia.org/wiki/Special:UserLogin/signup]] |
| [[Image:cyclicvoltammetrywaveform.jpg|thumb|300px|right|cyclic voltammetry waveform]] | | * Only registered users will be able to execute this rendering mode. |
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| In cyclic voltammetry, the electrode potential ramps linearly versus time as shown. This ramping is known as the experiment's scan rate (V/s). The potential is applied between the reference electrode and the working electrode and the current is measured between the working electrode and the counter electrode. These data are then plotted as current (''i'') vs. potential (''E''). As the waveform shows, the forward scan produces a current peak for any analytes that can be reduced (or oxidized depending on the initial scan direction) through the range of the potential scanned. The current will increase as the potential reaches the reduction potential of the analyte, but then falls off as the concentration of the analyte is depleted close to the electrode surface. If the [[redox couple]] is reversible then when the applied potential is reversed, it will reach the potential that will reoxidize the product formed in the first reduction reaction, and produce a current of reverse polarity from the forward scan. This oxidation peak will usually have a similar shape to the reduction peak. As a result, information about the redox potential and electrochemical reaction rates of the compounds are obtained.
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| For instance if the electronic transfer at the surface is fast and the current is limited by the [[diffusion]] of species to the electrode surface, then the [[current (electricity)|current]] peak will be proportional to the [[square root]] of the scan rate. This relationship is described by the [[Cottrell equation]]. The CV experiment then samples only a small portion of the solution, the material within the [[diffusion layer]].
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| | :<math forcemathmode="mathml">E=mc^2</math> |
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| == Characterization == | | <!--'''PNG''' (currently default in production) |
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| The utility of cyclic voltammetry is highly dependent on the analyte being studied. The analyte has to be redox active within the experimental potential window. It is also highly desirable for the analyte to display a reversible wave. A reversible wave is when an analyte is reduced or oxidized on a forward scan and is then reoxidized or rereduced in a predictable way on the return scan as shown in the first figure.
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| Even reversible couples contain polarization [[overpotential]] and thus display a hysteresis between absolute potential between the reduction (E<sub>pc</sub>) and oxidation peak (E<sub>pa</sub>). This overpotential emerges from a combination of analyte diffusion rates and the intrinsic activation barrier of transferring electrons from an electrode to analyte. A theoretical description of polarization overpotential is in part described by the [[Butler-Volmer equation]] and [[Cottrell equation]]. Conveniently in an ideal system the relationships reduces to, <math>|E_{pc}-E_{pa}|=\frac{57\text{ mV}}{n}</math>, for an n electron process.<ref name="Nicholson" />
| | <span style="color: red">Follow this [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering link] to change your Math rendering settings.</span> You can also add a [https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering-skin Custom CSS] to force the MathML/SVG rendering or select different font families. See [https://www.mediawiki.org/wiki/Extension:Math#CSS_for_the_MathML_with_SVG_fallback_mode these examples]. |
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| Reversible couples will display a ratio of the peak currents passed at reduction (i<sub>pc</sub>) and oxidation (i<sub>pa</sub>) that is near unity (1 = i<sub>pa</sub>/i<sub>pc</sub>). This ratio can be perturbed for reversible couples in the presence of a [[electrochemical reaction mechanism|following chemical reaction]], stripping wave, or nucleation event.
| | ==Demos== |
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| When such reversible peaks are observed [[bordwell thermodynamic cycle|thermodynamic information]] in the form of half cell potential E<sup>0</sup><sub>1/2</sub> can be determined. When waves are semi-reversible such as when i<sub>pa</sub>/i<sub>pc</sub> is less than or greater than 1, it can be possible to determine even more information especially kinetic processes like following [[electrochemical reaction mechanism|chemical reaction]].
| | Here are some [https://commons.wikimedia.org/w/index.php?title=Special:ListFiles/Frederic.wang demos]: |
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| When waves are non-reversible it is impossible to determine what their thermodynamic E<sup>0</sup><sub>1/2</sub> is with cyclic voltammetry. This E<sup>0</sup><sub>1/2</sub> can be determined, however it often requires equal quantities of the analyte in both oxidation states. When a wave is non-reversible cyclic voltammetry can not determine if the wave is at its thermodynamic potential or shifted to a more extreme potential by some form of [[overpotential]]. The couple could be irreversible because of a following chemical process, a common example for [[transition metal]]s is a shift in the geometry of the [[Complex (chemistry)|coordination]] sphere. If this is the case, then higher scan rates may show a reversible wave. It is also possible that the wave is irreversible due to a physical process most commonly some form of [[precipitation (chemistry)|precipitation]] as discussed below. Some speculation can be made in regards to irreversible waves however they are generally outside the scope of cyclic voltammetry.
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| == Experimental setup ==
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| | ** Orca: There is ongoing work, but no support at all at the moment [[File:Orca-mathml-example-1.wav|thumb|Orca-mathml-example-1]], [[File:Orca-mathml-example-2.wav|thumb|Orca-mathml-example-2]], [[File:Orca-mathml-example-3.wav|thumb|Orca-mathml-example-3]], [[File:Orca-mathml-example-4.wav|thumb|Orca-mathml-example-4]], [[File:Orca-mathml-example-5.wav|thumb|Orca-mathml-example-5]], [[File:Orca-mathml-example-6.wav|thumb|Orca-mathml-example-6]], [[File:Orca-mathml-example-7.wav|thumb|Orca-mathml-example-7]]. |
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| The method uses a [[reference electrode]], [[working electrode]], and [[counter electrode]] which in combination are sometimes referred to as a [[voltammetry|three-electrode setup]]. [[Electrolyte]] is usually added to the test solution to ensure sufficient conductivity. The combination of the solvent, electrolyte and specific working electrode material determines the range of the potential.
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| Electrodes are static and sit in unstirred solutions during cyclic voltammetry. This "still" solution method results in cyclic voltammetry's characteristic diffusion controlled peaks. This method also allows a portion of the [[analyte]] to remain after reduction or oxidation where it may display further redox activity. Stirring the solution between cyclic voltammetry traces is important as to supply the electrode surface with fresh analyte for each new experiment. The solubility of an analyte can change drastically with its overall charge. Since cyclic voltammetry usually alters the charge of the analyte it is common for reduced or oxidized analyte to [[precipitate]] out onto the electrode. This layering of analyte can insulate the electrode surface, display its own redox activity in subsequent scans, or at the very least alter the electrode surface. For this and other reasons it is often necessary to clean electrodes between scans.
| | To test the '''MathML''', '''PNG''', and '''source''' rendering modes, please go to one of the following test pages: |
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| Common materials for [[working electrode]]s include [[glassy carbon]], [[platinum]], and [[gold]]. These electrodes are generally encased in a rod of inert insulator with a disk exposed at one end. A regular working electrode has a radius within an order of magnitude of 1 mm. Having a controlled surface area with a defined shape is important for interpreting cyclic voltammetry results.
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| To run cyclic voltammetry experiments at high scan rates a regular working electrode is insufficient. High scan rates create peaks with large currents and increased resistances which result in distortions. [[Ultramicroelectrode]]s can be used to minimize the current and resistance.
| | ==Bug reporting== |
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| | If you find any bugs, please report them at [https://bugzilla.wikimedia.org/enter_bug.cgi?product=MediaWiki%20extensions&component=Math&version=master&short_desc=Math-preview%20rendering%20problem Bugzilla], or write an email to math_bugs (at) ckurs (dot) de . |
| The [[counter electrode]], also known as the auxiliary or second electrode, can be any material which conducts easily and won't react with the bulk solution. Reactions occurring at the counter electrode surface are unimportant as long as it continues to conduct current well. To maintain the observed current the counter electrode will often oxidize or reduce the solvent or bulk electrolyte.
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| [[Reference electrode]]s are a complex subject and worth investigating elsewhere.
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| == Variations == | |
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| In some experiments an electroactive species is fixed to the surface of the electrode, for instance in microparticle voltammetry.
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| Potentiodynamic techniques also exist that add low-amplitude ac perturbation to a potential ramp and measure variable response in a single frequency (ac voltammetry) or in many frequencies simultaneously ([[potentiodynamic electrochemical impedance spectroscopy]]).<ref>http://www.abc.chemistry.bsu.by/vi/</ref> The response in alternating current is two-dimensional – it is characterised by [[amplitude]] and [[phase (waves)|phase]]. The amplitude and phase depend differently on frequency for constituents of ac response attributed to different processes (charge transfer, diffusion, double layer charging, etc.). [[Frequency response]] analysis enables simultaneous monitoring of the various processes that contribute to the potentiodynamic ac response of electrochemical system.
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| == Distinctions == | |
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| Cyclic voltammetry is not a [[hydrodynamic technique]]. In a hydrodynamic technique flow is achieved at the electrode surface by stirring the solution, pumping the solution, or rotating the electrode as is the case with [[rotating disk electrode]]s and [[rotating ring-disk electrode]]s. These techniques target steady state conditions which appear the same scanned from the positive or the negative, thus limiting them to [[linear sweep voltammetry]].
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| == See also ==
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| * [[Voltammetry]]
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| * [[Electroanalytical methods]]
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| * [[Randles-Sevcik equation]]
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| == References ==
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| {{reflist}}
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| ==Further reading==
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| *{{Cite book
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| | edition = 2
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| | publisher = Wiley
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| | isbn = 0-471-04372-9
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| | last = Bard
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| | first = Allen J.
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| | coauthors = Larry R. Faulkner
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| | title = Electrochemical Methods: Fundamentals and Applications
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| | date = 2000-12-18
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| }}
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| * {{Cite book
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| | publisher = Elsevier Science
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| | isbn = 0-444-51958-0
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| | last = Zoski
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| | first = Cynthia G.
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| | title = [[Handbook of Electrochemistry]]
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| | date = 2007-02-07
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| }}
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| *{{Cite book
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| | edition = 2
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| | publisher = CRC
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| | isbn = 0-8247-9445-1
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| | last = Kissinger
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| | first = Peter
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| | coauthors = William R. Heineman
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| | title = Laboratory Techniques in Electroanalytical Chemistry, Second Edition, Revised and Expanded
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| | date = 1996-01-23
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| }}
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| ==External links==
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| * {{cite web | url = http://www2.chemistry.msu.edu/courses/cem419/cem372cyclicvoltammetry.pdf | title =CEM 372 Spring 2000 Cyclic voltammetry Lab Primer | publisher = [[Michigan State University]]}}
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| {{Electroanalytical}}
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| [[Category:Electroanalytical methods]]
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| [[de:Cyclovoltammetrie]]
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| [[fr:Voltampérométrie cyclique]]
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| [[it:Ciclovoltammetria]]
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| [[he:וולטמטריה ציקלית]]
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| [[nl:Cyclovoltammetrie]]
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| [[ja:サイクリックボルタンメトリー]]
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| [[zh:循環伏安法]]
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