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VOLTAMMETRY Presentation By Shashikant Wagh




INTRODUCTION: It is the branch of electrochemistry , we now call voltammetry . Developed from discovery of Polarography in 1922 by the Czech chemist Jaroslav Heyrovsky, for which he received Nobel Prize in 1959.

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The common characteristics of voltametric technique are that the involve the application of potential (E) to an electrode and monitoring of the resulting current (I) flowing through the electrochemical cell. In many cases the applied potential is varied or the current is monitored over a period of time (t) Thus all voltammetric techniques can be described as some function of E,I,t in short it is the study involve current and voltage. PRINCIPLE


Instrumentation The basic component of modern electrochemical system for voltammetry are a potentiostate computer and electrochemical cell in some cases the potentiostate and computer are housed package .


Potentiostate: a simple potentiostate circuit for three electrode cell with three operational Amplifier (OA) shown in fig.

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The three electrode system is used in the voltammetry for current in the range of microampere to miliampere with the use of micro size electrode, current are in the pico to nanoampere range, and thus two electrode are often used(that is counter and reference are tied together)

Types of Voltammetry:

Types of Voltammetry Linear sweep Voltammetry Staircase Voltammetry Square wave Voltammetry Cyclic Voltammetry

Cyclic Voltammetry::

Cyclic Voltammetry: Cyclic Voltammetry has become an important and widely used electro analytical technique in many areas of chemistry . It is rarely used for quantitative determination but it is widely used for the study of redox titration , and for obtaining stability of the reaction . This technique is based on varieng the applied potential at the working electrode in the both forward and reverse direction while monitoring the current. For example the potential. At the point scan would be reverse and run in the positive direction depending on the analysis on e full cycle, a partial cycle or a series cycle can be performed. The response obtained from C.V. can be very simple as shown in the fig. for a reversible redox system.

For reversible redox system:

For reversible redox system

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Cyclic voltammetry is carried out in quiescent solution to ensure diffusion control. The three electrode arrangement is used . Mercury film electrode are used because of there good negative potential range .Other working electrode includes gassy carbon ,platinum, gold ,graphite, carbon paste

Electrode used in cyclic Voltammetry:

Electrode used in cyclic Voltammetry Reference electrode. Counter electrode. Working electrode.

Reference electrode::

Reference electrode: A reference electrode should provide a reversible half-reaction with nernstian behavior be constant over time, and be easy to assemble and maintain. the most commonly used for aqueous solution are the calomel electrode, with potential determine by the reaction HgCl2(s)+2e-=2Hg+2c

Counter electrodes:

Counter electrodes In most voltammetric technique the analytical reaction at the electrode surface occur over very short time period and rarely produce any appreciable changes in bulk concentration of R or O . Thus ,isolation of the counter electrode from the sample is not normally necessary most often counter electrode consist of tin pt wire although Au.

Working electrode:

Working electrode The working electrode are of varies geometries and materials ranging from small Hg drops to flat pt disks. Mercury is useful because it display a wide negative potential range (because it is difficult to reduce hydrogen ion or water at the mercury surface)Its surface is readily generated by producing a new drop of film , and many metal ion can be reversibly reduce in it other commonly used electrode material are Au ,Pt ,.


Applications Determination of band gap of semiconductor. To determine the oxidation state of central metal atom in many metal complexes . To determine electron transfer where it is one or two electron transfer . It provides supplementary fluorescence spectrometry . It is widely used as a analytical technique for checking whether the analyte redox or not

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