digplanet beta 1: Athena
Share digplanet:

Agriculture

Applied sciences

Arts

Belief

Business

Chronology

Culture

Education

Environment

Geography

Health

History

Humanities

Language

Law

Life

Mathematics

Nature

People

Politics

Science

Society

Technology

Figure 1. Typical cyclic voltammogram where i_{pc} and i_{pa} show the peak cathodic and anodic current respectively for a reversible reaction.

Cyclic voltammetry or CV is a type of potentiodynamic electrochemical measurement. In a cyclic voltammetry experiment the working electrode potential is ramped linearly versus time. Unlike in linear sweep voltammetry, after the set potential is reached in a CV experiment the working electrode's potential is ramped in the opposite direction to return to the initial potential. These cycles of ramps in potential may be repeated as many times as desired. The current at the working electrode is plotted versus the applied voltage (i.e., the working electrode's potential) to give the cyclic voltammogram trace. Cyclic voltammetry is generally used to study the electrochemical properties of an analyte in solution.[1][2][3]

Experimental method[edit]

Figure 2. Cyclic voltammetry waveform.

In cyclic voltammetry, the electrode potential ramps linearly versus time in cyclical phases as shown in Figure 2. The rate of voltage change over time during each of these phases is known as the experiment's scan rate (V/s). The potential is applied between the working electrode and the reference electrode while the current is measured between the working electrode and the counter electrode. These data are plotted as current (i) vs. applied potential (E, often referred to as just 'potential'). In Figure 2, during the initial forward scan (from t0 to t1) an increasingly reducing potential is applied; thus the cathodic current will, at least initially, increase over this time period assuming that there are reducible analytes in the system. At some point after the reduction potential of the analyte is reached, the cathodic current will decrease as the concentration of reducible analyte is depleted. If the redox couple is reversible then during the reverse scan (from t1 to t2) the reduced analyte will start to be re-oxidized, giving rise to a current of reverse polarity (anodic current) to before. The more reversible the redox couple is, the more similar the oxidation peak will be in shape to the reduction peak. Hence, CV data can provide information about redox potentials and electrochemical reaction rates.

For instance, if the electron transfer at the working electrode surface is fast and the current is limited by the diffusion of analyte species to the electrode surface, then the peak current will be proportional to the square root of the scan rate. This relationship is described by the Cottrell equation. In this situation, the CV experiment only samples a small portion of the solution, i.e., the diffusion layer at the electrode surface.

Characterization[edit]

The utility of cyclic voltammetry is highly dependent on the analyte being studied. Most importantly, the analyte has to be redox active within the potential window to be scanned. It is also highly desirable for the analyte to display a reversible CV wave (such as that depicted in Figure 2), which is observed when all of the initial analyte can be recovered after a forward and reverse scan cycle.

Even reversible couples contain polarization overpotential and thus display a hysteresis between the reduction (Epc) and oxidation peak (Epa) potentials. This overpotential emerges from a combination of analyte diffusion rates and the intrinsic activation barrier of transferring electrons from the electrode to an analyte. A theoretical description of polarization overpotential is in part described by the Butler-Volmer equation and Cottrell equation equations. In an ideal system the relationships reduces to E_{pa}-E_{pc}=\frac{56.5\text{ mV}}{n} for an n electron process.[2]

Reversible couples have a ratio of peak currents at analyte oxidation (ipa) and reduction (ipc) that is near unity (ipa/ipc = 1). Even with a reversible couple this ratio can be perturbed away from unity in the presence of a subsequent chemical reaction that is triggered by the electron transfer, a stripping wave, or a nucleation event.

When a reversible peak is observed, thermodynamic information in the form of a half cell potential E01/2 can be determined. When waves are semi-reversible (ipa/ipc is close but not equal to 1), it may be possible to determine even more specific information (see electrochemical reaction mechanism).

When waves are non-reversible it is, in general, not possible to determine the thermodynamic potential E01/2 with cyclic voltammetry (when it is possible the system usually contains equal quantities of the analyte in both oxidation states). The redox couple could be irreversible because of a subsequent chemical process; a common example of this is a transition metal complex changing its coordination sphere geometry after an electron is transferred to or from it. If this is the case, then higher scan rates may show a reversible wave because the electron transfer cycles may be able to occur faster than the geometry change can. It is also possible that the wave is irreversible due to a physical process that takes the analyte products out of solution (see the precipitation example below). Some speculations can be made about irreversible waves, but in general they are outside the scope of cyclic voltammetry.

Experimental setup[edit]

A standard CV experiment uses a reference electrode, working electrode, and counter electrode. This combination is sometimes referred to as a three-electrode setup. An electrolyte is usually added to the sample solution to ensure sufficient conductivity. The solvent, electrolyte, and material composition of the working electrode will determine the potential range that can be accessed during the experiment.

The electrodes are immobile and sit in unstirred solutions during cyclic voltammetry. This "still" solution method gives rise to cyclic voltammetry's characteristic diffusion-controlled peaks. This method also allows a portion of the analyte to remain after reduction or oxidation so that it may display further redox activity. Stirring the solution between cyclic voltammetry traces is important in order to supply the electrode surface with fresh analyte for each new experiment. The solubility of an analyte can change drastically with its overall charge; as such it is common for reduced or oxidized analyte species to precipitate out onto the electrode. This layering of analyte can insulate the electrode surface, display its own redox activity in subsequent scans, or otherwise alter the electrode surface in a way that affects the CV measurements. For this reason it is often necessary to clean the electrodes between scans.

Common materials for the working electrode 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 well-defined shape is necessary for being able to interpret cyclic voltammetry results.

To run cyclic voltammetry experiments at very high scan rates a regular working electrode is insufficient. High scan rates create peaks with large currents and increased resistances, which result in distortions. Ultramicroelectrodes can be used to minimize the current and resistance.

The counter electrode, also known as the auxiliary or second electrode, can be any material which conducts current easily and will not 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.

Reference electrodes are a complex subject and worth investigating elsewhere.

Variations[edit]

In some experiments an electroactive species is fixed to the surface of the electrode; for instance, in microparticle voltammetry.

Potentiodynamic techniques also exist that add low-amplitude AC perturbations to a potential ramp and measure variable response in a single frequency (AC voltammetry) or in many frequencies simultaneously (potentiodynamic electrochemical impedance spectroscopy).[4] The response in alternating current is two-dimensional, characterized by both amplitude and phase. These data can be analyzed to determine information about different chemical 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 an electrochemical system.

Distinctions[edit]

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 electrodes and rotating ring-disk electrodes. Such techniques target steady state conditions and produce waveforms that appear the same when scanned in either the positive or negative directions, thus limiting them to linear sweep voltammetry.

Applications[edit]

Cyclic voltammetry (CV) has become an important and widely used electroanalytical technique in many areas of chemistry. It is often used to study a variety of redox processes, to determine the stability of reaction products, the presence of intermediates in redox reactions, reaction [5] and electron transfer kinetics,[6] and the reversibility of a reaction.[7] CV can also be used to determine the electron stoichiometry of a system, the diffusion coefficient of an analyte, and the formal reduction potential of an analyte, which can be used as an identification tool. In addition, because concentration is proportional to current in a reversible, Nernstian system, the concentration of an unknown solution can be determined by generating a calibration curve of current vs. concentration. [8][9][10][11][12][13]

This latter application is gaining interest in the field of cellular biology where it is used to measure the concentrations of various chemicals in the cells of organisms, including living ones.[14]

See also[edit]

References[edit]

  1. ^ Bard, Allen J.; Larry R. Faulkner (2000-12-18). Electrochemical Methods: Fundamentals and Applications (2 ed.). Wiley. ISBN 0-471-04372-9. 
  2. ^ a b Nicholson, R. S.; Irving. Shain (1964-04-01). "Theory of Stationary Electrode Polarography. Single Scan and Cyclic Methods Applied to Reversible, Irreversible, and Kinetic Systems.". Analytical Chemistry 36 (4): 706–723. doi:10.1021/ac60210a007. 
  3. ^ Heinze, Jurgen (1984). "Cyclic Voltammetry-"Electrochemical Spectroscopy". New Analytical Methods (25)". Angewandte Chemie International Edition in English 23 (11): 831–847. doi:10.1002/anie.198408313. 
  4. ^ http://www.abc.chemistry.bsu.by/vi/
  5. ^ Nicholson, R.S. (1965). "Theory and Application of Cyclic Voltammetry for Measurement of Electrode Reaction Kinetics". Anal.Chem. 37: 1351–1355. doi:10.1021/jp9828437. 
  6. ^ DuVall, Stacy DuVall; McCreery,Richard (1999). "Control of Catechol and Hydroquinone Electron-Transfer Kinetics on Native and Modified Glassy Carbon Electrodes". Anal.Chem. 71: 4594–4602. doi:10.1021/ac990399d. 
  7. ^ Bond, Alan M.; Feldberg,Stephen (1998). "Analysis of Simulated Reversible Cyclic Voltammetric Responses for a Charged Redox Species in the Absence of Added Electrolyte". J.Phys.Chem. 102: 9966–9974. doi:10.1021/ac60230a016. 
  8. ^ Carriedo, Gabino (1988). "The use of cyclic voltammetry in the study of the chemistry of metal carbonyls". J.Chem.Educ. 65. 
  9. ^ Sanghavi, Bankim; Srivastava, Ashwini (2010). "Simultaneous voltammetric determination of acetaminophen, aspirin and caffeine using an in situ surfactant-modified multiwalled carbon nanotube paste electrode". Electrochimica Acta 55: 8638–8648. doi:10.1016/j.electacta.2010.07.093. 
  10. ^ Sanghavi, Bankim; Mobin, Shaikh; Mathur, Pradeep; Lahiri, Goutam; Srivastava, Ashwini (2013). "Biomimetic sensor for certain catecholamines employing copper(II) complex and silver nanoparticle modified glassy carbon paste electrode". Biosensors and Bioelectronics 39: 124–132. doi:10.1016/j.bios.2012.07.008. 
  11. ^ Sanghavi, Bankim; Srivastava, Ashwini (2011). "Simultaneous voltammetric determination of acetaminophen and tramadol using Dowex50wx2 and gold nanoparticles modified glassy carbon paste electrode" 706. pp. 246–254. doi:10.1016/j.aca.2011.08.040. 
  12. ^ Sanghavi, Bankim; Srivastava, Ashwini (2011). "Adsorptive stripping differential pulse voltammetric determination of venlafaxine and desvenlafaxine employing Nafion–carbon nanotube composite glassy carbon electrode". Electrochimica Acta 56: 4188–4196. doi:10.1016/j.electacta.2011.01.097. 
  13. ^ Mobin, Shaikh; Sanghavi, Bankim; Srivastava, Ashwini; Mathur, Pradeep; Lahiri, Goutam (2010). "Biomimetic Sensor for Certain Phenols Employing a Copper(II) Complex". Analytical Chemistry 82: 5983–5992. doi:10.1021/ac1004037. 
  14. ^ Wightman, R. Mark (2006). "Probing Cellular Chemistry in Biological Systems with Microelectrodes". Science 311 (5767): 1570–1574. doi:10.1126/science.1120027. PMID 16543451. 

Further reading[edit]

  • Bard, Allen J.; Larry R. Faulkner (2000-12-18). Electrochemical Methods: Fundamentals and Applications (2 ed.). Wiley. ISBN 0-471-04372-9. 
  • Zoski, Cynthia G. (2007-02-07). Handbook of Electrochemistry. Elsevier Science. ISBN 0-444-51958-0. 
  • Kissinger, Peter; William R. Heineman (1996-01-23). Laboratory Techniques in Electroanalytical Chemistry, Second Edition, Revised and Expanded (2 ed.). CRC. ISBN 0-8247-9445-1. 
  • Gosser, David K. (1993-09-20). Cyclic Voltammetry Simulation and Analysis of Reaction Mechanisms. VCH. ISBN 1-56081-026-2. 
  • Compton, Richard D.; Craig E. Banks (2010-11-15). Understanding Voltammetry (2 ed.). Imperial College Press. ISBN 1848165854. 

External links[edit]


Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Cyclic_voltammetry — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
948 videos foundNext > 

Basics of Cyclic Voltammetry

Cyclic Voltammetry Technique : An Introduction,Theoretical.

Voltammetry

A basic description of voltammetry for Chem 2821 at UVa.

Cyclic Voltammogram

Cyclic Voltammogram.

Cyclic Voltammetry of Ferricyanide solution using KCl as supporting electrolyte.

Cyclic Voltammetry of Ferricyanide solution using NOVA 1.7 Interface.-Practical.

Cyclic Voltammetry

My First Project.

Cyclic Voltammetry - ACM Instruments

Demonstration of Cyclic Voltammetry setup using ACM Instruments sequencer software.

Cyclic Voltammetry Simulation Video

A video showing the simulation results of a cyclic voltamagram of quinones, which undergo two successive one electron transfers in non-aqueous media.

Cyclic Voltammetry Recipe Tutorial

For all software downloaded prior to EZware 2013 v 7 software. Step by step instruction on how to design and run a cyclic voltammetry recipe using NuVant Sys...

Cyclic Voltammetry Analysis - ACM Instruments

Demonstration of Cyclic Voltammetry using ACM Instruments Analysis software.

Electrochemistry eDAQ Potentiostat, Cyclic Voltammetry CV in EChem Software

eDAQ manufactures a range of potentiostats, electrodes and electrochemistry accessories. This includes the ER466 Integrated Potentiostat, the EA362 Dual Pico...

948 videos foundNext > 

1 news items

 
separationsNOW.com
Sun, 26 Oct 2014 05:11:15 -0700

The electrochemical parameters of the compounds, studied by cyclic voltammetry, indicated that atrazine and HPPH did not show a current peak over the range of potentials in the mobile phase. More promisingly, bentazone, carbamazepine and phenytoin ...
Loading

Oops, we seem to be having trouble contacting Twitter

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!

Searchlight Group

Digplanet also receives support from Searchlight Group. Visit Searchlight