Cyclic voltammetry is an electroanalytical technique that measures current during redox reactions at an electrode. It involves scanning the potential of a working electrode versus a reference electrode and measuring the current. The potential is ramped from an initial value to a set switching potential and back to the initial value. This process is repeated in cycles. A cyclic voltammogram plots the current response of the working electrode versus the applied potential and provides information about redox potentials and reaction reversibility. Reversible reactions produce symmetrical peaks while irreversible reactions have wider separation between peaks. Cyclic voltammetry is useful for studying electrode reaction mechanisms and kinetics.

1. CYCLIC
VOLTAMMETRY
S U B M I T T E D TO : -
D R . M A N J U L ATA PA R I H A R
SUBMITTED BY :-
DALPAT SINGH

2. BASIC INTRODUCTION TO VOLTAMMETRY :-
• Voltammetry is concerned with the study of voltage-current-time
relationships during electrolysis carried out in a cell. In simple
words, The technique commonly involves studying the influence
changes in applied voltage on the current flowing in the cell.
• It is used to determine substances in solution which can be
reproducibly reduced or oxidized at an electrode surface.
• The procedure normally involves the use of a cell with an
of three electrodes -
(1) a working electrode at which the electrolysis under
investigation takes place. it should be completely polarizable so
that the current which flows through the electrode is proportional to
the concentration.
(2) a reference electrode which is used to measure the potential
of the working electrode.
(3) an auxiliary electrode or counter current electrode which,
together with the working electrode, carries the electrolysis current.

3. • The current-voltage graph which may be drawn is known as a
voltammogram.
• If we use dropping mercury electrode as working electrode and
pool of mercury as auxiliary electrode then this technique is
referred as Polarography.
• Why modified voltammetry is introduced ?
(1) Quantitative polarography is limited at best to solutions with
electrolytes at concentrations greater than 10-5 M .
(2) the half wave reduction potential difference between two
ions must be at least 200mV if the reduction waves are to be
separated.
These limitations are largely due to the condenser current
associated with the charging of each mercury drop as it forms.
• Pulse polarography, rapid scan polarography , sinusoidal
polarography and Cyclic voltammetry are types of modified
voltammetry.

4. CYCLIC VOLTAMMETRY :-
• Cyclic Voltammetry is a type of modified voltammetry in which a
very fast scan is carried out in two directions , 0 to V and back
down to 0.
• In a cyclic voltammetry experiment the working electrode
potential is ramped linearly versus time in cyclical phases.
• Cyclic voltammetry takes the three
electrode setup; when working
electrode reaches a set potential,
the ramp is inverted. This inversion
can happen multiple times during a
single experiment.
• Normally this process is conducted
using electrodes with a small
surface area in unstirred solutions,
producing a very small redox
current. This means ohmic drop IR is
small, even for the poorly
conducting solutions.• The low capacitance completely eliminates any contribution to the
diffusion current and allow fast scan rate ( up to 10KV s-1 ).

5. BASIC PRINCIPLES OF CYCLIC VOLTAMMETRY:-
• The limiting current occurs because the reduction is limited by the
rate at which ions reach the surface of the electrode. And there are
three conditions to the limiting current –
ilimit = id + iC + iM
• Migration current :- electro active material reaches the surface of
the electrode under the influence of an applied potential. Heyrovsky
showed that the migration current can be practically eliminated if an
indifferent electrolyte is added to the solution in a concentration so
large that its ions carry essentially all the current and it doesn’t
react with the electro active main species.
• Convection current:- if ions are transported toward the electrode
surface by mechanical means such as stirring in the solution then
this will affect the limiting current. To eliminate this we use
stationary solution system like dropping mercury electrode and we
can also use hydrodynamic voltammetry in which the solution is in
continual and constant motion.

6. • Diffusion current :- when an excess of supporting electrolyte is present in
the unstirred solution then the electrical force on the reducible ions is
nullified; this is because the migration current and the convection current
is eliminated. So under this conditions the limiting current is almost solely
a diffusion current.
ilkovic gives this equation which govern the diffusion current :-
id = 607nD1/2Cm2/3t1/6
Where id = the average diffusion current in microamperes
n = no. of electrons consumed in the reduction of one molecule
D = the diffusion coefficient of the substance
C = concentration of analyte in mol L-1
m = the rate of flow of mercury from the DME in mgs-1
t = drop time in seconds
• This equation is slightly temperature dependent.
• Ilkovic equation neglects the effect of the curvature of mercury drop
and this may be allowed for by multiplying the right hand side of the
equation by (1+AD1/2t1/6m-1/3), where A is a constant having value 39.
• The product m2/3t1/6 is important because it permits results with
different capillaries.

7. • Residual current :- If a current voltage curve is determined for a
solution containing ions with strongly negative reduction potential
, a small current will flow before the decomposition of the
solution begins. This current increases linearly with the applied
potential.
• Polarographic maxima :- the streaming movement of the diffusion
layer is responsible for the current maximum. Current voltage
curve exhibits maxima with DME so to eliminate it we use
maximum suppressors like gelatin , dyestuff (fuchsine solution) etc.
.
these are the surface active substances and they form a absorbed
layer on the aqueous side of the mercury solution interface which
resists compression and prevent the streaming of movement of
diffusion layer.
• Half wave potential :- The potential at a polarized electrode obeys
the Nernst equation and the concentrations of electro active
species is directly related to the diffusion current.

8. Cyclic Voltammogram :-

9. • In cyclic voltammetry, the electrode potential ramps linearly versus time
in cyclical phases.
• 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 measured
between the working electrode and the reference electrode, while the
current is measured between the working electrode and the counter
electrode.
• 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.
• The counter electrode, also known as the auxiliary or second electrode,
can be any material that conducts current easily and will not react with
the bulk solution.
• Electrolyte :- The electrolyte ensures good electrical conductivity . For
aqueous solutions, many electrolytes are available, but typical ones are
alkali metal salts of perchlorate and nitrate. In no aqueous solvents, the
range of electrolytes is more limited, and a popular choice
is tetrabutylammonium hexafluorophosphate.
EXPERIMENTAL SETUP:-

10. • The current at the working electrode is plotted versus the
applied voltage to give the cyclic voltammogram trace.
• Since the scan is in two directions, two curves are normally seen;
a normal cathodic reduction wave and an anodic wave as the
voltage reverses. Curves are equal in magnitude and
approximately vertically aligned.
• This indicates that the electrode process is a fast reversible
Cyclic Voltammogram :-

11. CRITERIA FOR THE REVERSIBILITY OF
ELECTROCHEMICAL REACTIONS :-
• Electrochemical reversibility describes the rate at which the electron
transfer occurs between the working electrode and the solution
redox species.
• Electrochemically reactions are of three types depending on their
electrochemical behavior :-
(1) Reversible electrochemical reactions :- A redox reaction can be
termed as reversible electrochemical reaction, if species swiftly
exchange electrons with the working electrode. This type of reaction
can be recognized from a cyclic voltammogram by calculating the
potential difference among the two peaks potential.
The given equation concerns to an electrochemically reversible system:
Where n = No. of electrons involved in the electrochemical reaction ,
Delta Ep = difference between the potential of anodic peak and
cathodic peak

12. (2)Irreversible electrochemical reactions :-If there take place a very slow
electron exchange between the working electrode and the redox specie
then it is termed as irreversible electrochemical reaction. The separation
of peak is greater than 0.058/n V in given formula
(3) Quasi-reversible electrochemical reactions :- Quasi-reversible
process exhibits intermediate behavior between irreversible and
reversible process. In this process, both mass transfer and current
transfer control the process.
• we can also define it by the ratio of charge transfer to mass
transfer.
According to bard and faunlkner :-
where Λ = electrochemical reversibility parameter
k0 = electrochemical facility is a measure of the ease of
electron exchange
(Dfv)0.5 = mass transfer

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